a study is run to estimate the mean total cholesterol level in children 9-11 years of age. a random sample of 169 participants is selected and their mean total cholesterol levels is 161.5. assume the population standard deviation is 19.5. give the following information for a 95% confidence interval for the mean cholesterol.
Sample mean =
Standard Deviation =
Sample size =
Do you use Z or t?
Z or t =
Standard Error (Rounded to nearest tenth)=
Margin of Error (Rounded to nearest tenth) =
Lower limit (Rounded to nearest tenth) =
Upper limit (Rounded to nearest tenth) =

Making r the subject of formula in this equation A = V²/r gives r = V²/A.

In Mathematics and Science, the centripetal acceleration of a physical object (body) can be calculated by using the following mathematical expression:

A = V²/r

Where:

In this exercise, you are required to make radius (r) the subject of formula. Therefore, by making radius (r) the subject of formula, we have the following:

Radius, r = V²/A

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Therefore, the function that matches the mosquito counts is'(w) = 8([tex]1.5^{w}[/tex]).

by the question.

To determine which function matches the mosquito counts, we can plot the given data points on a graph and see which function fits the curve. Here are the counts for the first few weeks:

Week Mosquito Count

0 8

1 20

2 50

3 125

4 312

Plotting these points on a graph with weeks on the x-axis and mosquito count on the y-axis, we get:

mosquito graph

Looking at the graph, we can see that the curve increases rapidly and seems to be exponential. This rule out option A (which is linear), leaving us with options B, C, and D.

To determine which of these options matches the data, we can try plugging in the week numbers and seeing which one gives us values close to the actual counts. We can also use a calculator or graphing technology to help us with this.

Option B gives us the following mosquito counts for the first five weeks:

Week Mosquito Count

0            8

1         19.5

2        47.25

3       114.19

4       276.32

Option C   gives us:

Week Mosquito Count

0       8

1        12

2       18

3       27

4       40.5

Option D is not a function of mosquito counts with weeks as the input variable, so we can rule it out.

Comparing the values from options B and C to the actual counts, we can see that option C is the closest match.

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Let's assume that the measure of angle BAC is less than or equal to the measure of angle ABC.

Since AB = AC, then angles BAC and BCA are also equal. Let's denote the measure of angle BAC as x, then the measure of angle ABC and angle BCA is also x.

According to the triangle inequality theorem, the sum of any two sides of a triangle must be greater than the third side. In our case, we have:

AB + BC > AC

AB + 24 > AC

2AB + BC > 2AC

2AB + 24 > 2AC

2AB > 2AC - 24

AB > AC - 12

Since AB = AC, then AC - 12 < AB = AC, which means AC < AC + 12. This is a contradiction, and therefore our assumption that the measure of angle BAC is less than or equal to the measure of angle ABC is false.

Therefore, we can conclude that Angle BAC > Angle ABC.

The equation of the required line in slope-intercept form is y = -1/4x + 8.

Here are the steps to find the equation of the line:

Step 1: Find the slope of the given line in slope-intercept form

y = mx + c

-4x + y = 43 ⇒ y = 4x + 43... (1)

Here, the slope (m1) of the given line is 4.

Step 2: Find the slope of the required line as the two lines are perpendicular to each other.

m1 × m2 = -1

[As the given line and the required line are perpendicular to each other]

4 × m2 = -1 ⇒ m2 = -1/4

So, the slope (m2) of the required line is -1/4.

Step 3: Write the equation of the required line in point-slope form.

y - y1 = m(x - x1)

[Using the point-slope formula]

Let (x1, y1) = (-8, 10)m = -1/4

Putting the values in the above formula, we get

y - 10 = -1/4(x - (-8)) ⇒ y - 10 = -1/4(x + 8)... (2)

Step 4: Simplify the above equation to get the required equation of the line in slope-intercept form.

y - 10 = -1/4x - 2 ⇒ y = -1/4x + 8... (3)

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Jordy's first error in his proof is option (c) Jordy established all necessary conditions, but then used an inappropriate congruence criterion

Jordy's first error in his proof is that he used an inappropriate congruence criterion to prove that the two triangles are congruent. He established all necessary conditions, but AAA congruence is only valid for proving congruence of triangles in certain special cases, such as when the triangles are similar.

In general, AAA congruence is not a valid congruence criterion. This highlights the importance of choosing the correct congruence criterion when proving that two triangles are congruent, as using an invalid or inappropriate criterion can lead to an incorrect conclusion.

Therefore, the correct option is (c) Jordy established all necessary conditions, but then used an inappropriate congruence criterion

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Let X and Y be two matrices in A. We can write X = ((x,0),(0,y)) and Y = ((z,0),(0,w)). If we add X and Y, we get((x+z,0),(0,y+w)). The sum is in A if and only if x+z+y+w=5.

Subset of M2x2:A subset of M2x2 is a set that contains some elements of M2x2.

A subset of M2x2 can be considered as a subspace if it meets the following conditions:

To determine if A is a subspace of M2x2, we need to verify that A meets the following conditions:

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The force equation for the system is F = bV - bF, where F is the force of friction, V is the velocity of the object, and b is the coefficient of viscous friction.

Viscous friction is a force that acts to oppose the motion of an object moving through a fluid or solid. The amount of friction experienced is determined by the coefficient of viscosity, which is a measure of how easily the two surfaces move against each other. In this equation, bV is the force generated by the object's motion, and b

F is the opposing force of friction. Together, these two forces determine the net force acting on the object.

Viscous friction can be very important in understanding the behavior of a system. It helps us to understand how much energy is needed to move objects, as well as how quickly they will accelerate.

Viscous friction can also cause objects to slow down over time, as the energy it takes to move them is continually being lost to friction. Understanding the force equation for a system helps us to better predict and understand its behavior.

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Answer:

The given equation is in vertex form y = a(x - h)^2 + k, where (h, k) is the vertex of the parabola. Comparing the given equation with the vertex form, we have a = -3, h = -3 and k = 4.

Since a = -3 < 0, the parabola opens downwards and has a maximum point.

To find the maximum value of y, we need to evaluate y at the x-coordinate of the vertex:

x = -3

y = -3(-3+3)^2 + 4 = 4

Therefore, the parabola y = -3(x+3)2 + 4 contains a maximum point and the maximum value of y is 4.

Hence, the answer is option C

Answer:

C)  Maximum point; 4

Step-by-step explanation:

Given parabola:

[tex]y=-3(x+3)^2+4[/tex]

The given parabola is in vertex form:

[tex]\boxed{y = a(x - h)^2 + k}[/tex]

where:

By comparing the given equation with the vertex form, we can see that:

As a < 0, the parabola opens downwards. Therefore, the vertex of the parabola is a maximum point.

The vertex of the parabola is (h, k) = (-3, 4).

Therefore, the maximum value of y is 4, which occurs at x = -3.

The area of the composite figure with the given subshapes is 99.13 square feet

Given the following parameters:

The composite figure with the following shapes

Semi-circle with diameter 8 ft

Triangle with base of 8 ft and height of 6 feet

Rectangle of 10 by 5 feet

The area of the composite figure is the sum of the individual areas

So, we have

Area = 1/2 * π(8/2)² + 1/2 * 8 * 6 + 10 * 5

Evaluate

Area = 99.13

Hence, the area is 99.13 square feet

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Answer:

p ≥ 228

Step-by-step explanation:

p ≥ 228

This inequality means the Bowlers have to score at least 228 points to move on.

Hope this helped!

The complete table for the amount balance, A when P dollars is invested at rate r for t years and compounded n times per year is present in above figure 2.

The compound interest formula is written as A = P( 1 + r/n)ⁿᵗ

where, A--> total Amount of money after t years

P --> Principal

r --> Annual rate of interest (as a decimal)

t --> Number of years:

n--> number of times interest is compounded per year

Here, principle, P = $1300, rate of interest, r = 8.5% = 0.085 , time periods, t = 11 years. We have to complete the above table for compound interest.

Case 1: n = 1

Substitute the known values in above formula, A = 1300( 1 + 0.085/1)¹¹

= 1300( 1.085)¹¹

= 3,189.12

Case 2: n = 2

A = 1300( 1 + 0.085/2)²²

= 1300( 2.085/2)²²

= 1300( 1.0425)²²

= 3,248.01

I'll let you work out the cases where n = 4, 12 and 365 since all you need to do is place those in for n as done in the 1st 2 cases. For the Compounded continuously case, the formula becomes,

[tex] A = Pe^{rt}[/tex]

Where: A-> Total amount of money after t years

P --> Principal Amount

e --> Natural log constant:

r = Annual rate of interest (as a decimal)

Case: Continuous: e = 2.71828 (approx), r = 0.085

A = 1300( 2.71828)⁰·⁰⁸⁵⁽¹¹⁾

= 1300(e)⁰·⁹³⁵ = 3,311.34

Hence, required value is $3,311.3775.

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Complete question :

The above table completes the question.

Complete the table by finding the balance A when P dollars is invested at rate r for t years and compounded n times per year. (Round your answers to the nearest cent. ) P = $1300, r = 8. 5%, t

= 11 years

Therefore, the total number of ways to select 2 cooked and 3 uncooked eggs is 210 ways.

In mathematics, a combination is a way of selecting items from a collection, such that (unlike permutations) the order of selection does not matter. In other words, a combination is a selection of items from a larger set, without regard to the order in which they are chosen. The number of combinations of size r that can be chosen from a set of n elements is denoted by the symbol C(n, r), and is given by the formula:

C(n, r) = n! / (r! * (n-r)!)

where n! (pronounced "n factorial") is the product of all positive integers up to n, and r! is the product of all positive integers up to r.

Here,

a) To find the number of ways to select 2 cooked or 3 uncooked eggs, we need to use the combination formula, which is:

ⁿCₓ= n! / r!(n-r)!

where n is the total number of eggs, r is the number of eggs we want to select, and ! represents factorial.

For 2 cooked eggs, we can select them in:

⁷C₂ = 7! / 2!(7-2)! = 21 ways

For 3 uncooked eggs, we can select them in:

⁵C₃ = 5! / 3!(5-3)! = 10 ways

Therefore, the total number of ways to select 2 cooked or 3 uncooked eggs is:

21 + 10 = 31 ways

b) To find the number of ways to select 2 cooked and 3 uncooked eggs, we need to use the product rule of counting. That is, we need to multiply the number of ways to select 2 cooked eggs and 3 uncooked eggs.

The number of ways to select 2 cooked eggs is:

⁷C₂ = 21 ways

The number of ways to select 3 uncooked eggs is:⁵C₃ = 10 ways

Therefore, the total number of ways to select 2 cooked and 3 uncooked eggs is:

21 x 10 = 210 ways

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The compounding formula is used to create the quarterly compounding formula. To the nearest cent, the compounded balance is $ [tex]12,832.27.[/tex]

To reflect the quarterly interest computation as the only change, the interest rate is increased by 4*2.

[tex]A = P(1 + r/n)(nt)[/tex]

Assume that we have a $  [tex]10,000[/tex] Initial investment, a 6% yearly interest rate, and a 5-year investment period. We have n = 4 and t = 5 since the interest is compounded every three months.

Plugging in these values, we get:

[tex]A = 10,000(1 + 0.06/4)(4*5)[/tex]

[tex]= 10,000(1.015)^20[/tex]

[tex]= 12,835.72[/tex]

Hence, the final balance is $ [tex]12,835.72[/tex] to the nearest penny.

If the money is compounded continually, we may use the following formula to determine the balance:

[tex]A = Pe(rt)[/tex]

With the identical values as before, we obtain:

[tex]A = 10,000e(0.06 \times5)[/tex]

[tex]= 10,000e(0.3)[/tex]

[tex]= 12,832.27[/tex]

Therefore, So the balance, to the nearest cent, is $ [tex]12,832.27.[/tex]

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Hence, the abbreviated formula is -7 + 0i, or just -7.

The terms in the parentheses can be immediately simplified. So, we can carry out the operations indicated by the brackets in the following order: multiplication, addition, subtraction, division. Note: The brackets should be shortened in the following order: (),, []. Simplify: 14 + (8 - 2 3) for Example 2.

We must combine like terms in order to make the phrase simpler.

First, we can individually merge the real and made-up parts:

The genuine parts add out to -3 - 4 = -7.

i - i = 0 is the imaginary part's total.

Hence, the abbreviated formula is -7 + 0i, or just -7.

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Complete question:

Please simplify the following expression while performing the given operation. (-3+i)+(-4-i)

Answer: 240

You multiply them. 6x4x10 :)

The number of different outfits made by Alyssa as per the given number of shirt , skirts and shoes is equal to 240 outfits.

To find the number of possible outfits Alyssa can make, you multiply the number of choices for each item of clothing:

Number of shirts = 6

Number of skirts = 4

Number of pairs of shoes = 10

Substitute the values and multiply with each other

Total number of possible outfits

= 6 (shirts) × 4 (skirts) × 10 (shoes)

= 240 outfits.

Therefore, Alyssa can make 240 different outfits using her 6 shirts, 4 skirts, and 10 pairs of shoes.

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Answer:

C. (45+2+7)-(43+2+7) / 5+3

Step-by-step explanation:

To find the average rate of change of h(x) on the interval -3 ≤ x ≤ 5, we need to evaluate the following expression:

[h(5) - h(-3)] / (5 - (-3))

We have:

h(5) = 4(5) + 2 + 7 = 29

h(-3) = 4(-3) + 2 + 7 = -5

Substituting into the formula, we get:

[29 - (-5)] / (5 - (-3)) = 34 / 8 = 17 / 4

Therefore, the expression that gives the average rate of change of the function h(x) on the interval -3 ≤ x ≤ 5 is:

C. (45+2+7)-(43+2+7) / 5+3

The inequality that represents x is x ≥ 0/

The basic square rοοt οperatiοn. (οften knοwn as the "square rοοt functiοn") is a mapping that applies tο the set οf nοnnegative real numbers. The square rοοt functiοn, in geοmetric terms, cοnverts a square's area tο its side length.

The οrder οf pοsitive numbers is preserved by the square functiοn: greater numbers have larger squares. The square, then, is a mοnοtοnic functiοn οn the range [0, +]. With negative numbers, absοlute values are mοre significant than squares, making it a mοnοtοnically decreasing functiοn οn [(, 0]].

Here, The domain of the graph is domain : [0, +∞)

With this, we can clearly state that 0 < x < +∞

Thus, The inequality that represents x is x ≥ 0

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[tex]3[/tex] days [tex]0[/tex] hours. The answer is three because the function [tex]W[/tex] that solves the differential equation gives the number of weeds in a large garden.

A number is calculated and represented using a decimal, which is an algebra quantity. In handwriting, numerical symbols like "3" are used to represent numbers. A counting system is a logical way of expressing numbers that uses digits or symbols to represent them.

Vets Day and Memorial Day are commonly celebrated on November 11 in the United States and overseas, respectively. The history, mythology, and mathematical importance of this particular time and date are all explained here.

[tex]\frac{dw}{dt}=\frac{1}{12}(-318+24W)[/tex]

[tex]\frac{d^{2}W }{dt^{2} }=\frac{d}{dt}[\frac{1}{12} (-318+24W)][/tex]

When [tex]W=14, \frac{dW}{dt}[/tex]

[tex]=\frac{1}{12}(-318+24*14)[/tex]

[tex]=\frac{18}{12}=1.5[/tex]

[tex]=2\frac{dW}{dt}=2*1.5[/tex]

[tex]=3[/tex]

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The complement of the angle is 38 degrees and the supplement of the angle is 128 degrees.

The given angle is

Angle = 52 degrees

To find the complement of an angle, we need to subtract its measure from 90 degrees.

Therefore, the complement of an angle with a measure of 52 degrees is:

90 degrees - 52 degrees = 38 degrees

So, the complement of the angle shown is 38 degrees.

To find the supplement of an angle, we need to subtract its measure from 180 degrees.

Therefore, the supplement of an angle with a measure of 52 degrees is:

180 degrees - 52 degrees = 128 degrees

So, the supplement of the angle shown is 128 degrees.

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Answer: Quadratic polynomial.

Step-by-step explanation: Polynomials with 2 as the degree.

Answer: So that means the answer is $112.5

Step-by-step explanation:Percent of Discount is 80%. Sale Price is $90. The original price,. = 90 x 100 / 80. = 9000/80. = 112.5. Therefore, $112.5 is the original price.

YES THIS IS RIGHT!!!!

Thursday’s high temperature was 6.5 degrees more than Wednesday’s high temperature.

Average temperature is calculated as (Monday's temperature plus Tuesday's temperature plus Wednesday's temperature plus Thursday's temperature)/Total days.

Temporary for Monday and Tuesday plus Temperatures for Wednesday and Thursday.

The sum of the temperatures for Monday, Tuesday, Wednesday, and Thursday is equal.

As stated, the 6.5 degree average for the days of Tuesday, Wednesday, Thursday, and Friday.

using the formula no.

Average temperature is equal to (Tuesday's temperature plus Wednesday's temperature plus Thursday's temperature plus Friday's temperature)/Total days.

Thus, Thursday’s high temperature was 6.5 degrees more than Wednesday’s high temperature.

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the complete question is

Write a positive or negative number to represent each change in the high temperature.

1. Tuesday’s high temperature was 4 degrees less than Monday’s high temperature. ?

2. Wednesday’s high temperature was 3.5 degrees less than Tuesday’s high temperature. ?

3. Thursday’s high temperature was 6.5 degrees more than Wednesday’s high temperature. ?

4. Friday’s high temperature was 2 degrees less than Thursday’s high temperature. ?

16. The equatiοn οf the line in slοpe-intercept fοrm that passes thrοugh the pοint (-6, 5) and is parallel tο x + 2y = 14 is y = (-1/2)x + 2.

The equatiοn οf a straight line is y = mx + c, y = m x + c m is the gradient and c is the height at which the line crοsses the y -axis, alsο knοwn as the y -intercept.

16. Tο write the equatiοn οf a line in slοpe-intercept fοrm, we need tο find the slοpe and the y-intercept οf the line.

Tο find the slοpe οf the line, we can rewrite the equatiοn x + 2y = 14 in slοpe-intercept fοrm y = mx + b by sοlving fοr y:

x + 2y = 14

2y = -x + 14

y = (-1/2)x + 7

The slοpe οf the line is -1/2.

Since the line we want tο find is parallel tο this line, it will have the same slοpe οf -1/2.

Nοw we can use the pοint-slοpe fοrm οf the equatiοn οf a line tο find the equatiοn οf the line that passes thrοugh the pοint (-6, 5) with a slοpe οf -1/2:

y - y1 = m(x - x1)

where (x1, y1) is the pοint (-6, 5), and m is the slοpe, -1/2.

y - 5 = (-1/2)(x - (-6))

y - 5 = (-1/2)x - 3

y = (-1/2)x + 2

17. The equation perpendicular to y = -(2/3)x + 4, passing through (-4, 6)

perpendicular equations slope would be negative reciprocal to the current line.

The slope in y = -(2/3)x + 4, is m = -(2/3),

The negative reciprocal of -(2/3) is 3/2

Now, applying the x and y values in pοint-slοpe fοrm

y - 6 = 3/2(x - (-4))

y =  3/2(x+4) + 6

y =  (3/2)x + 6 + 6

y =  (3/2)x + 12

18. Since the line we want tο find is parallel tο this line, it will have the same slοpe.

Lets find the slope using slope formula

[tex]\rm m = \dfrac{y_2 - y_1}{x_2 - x_1}[/tex]

[tex]\rm m = \dfrac{0 - (-1)}{2 - (-1)}[/tex]

[tex]\rm m = \dfrac{1}{3}[/tex]

Now, using the point slope form

y - 1 = 1/3(x - 3)

y = 1/3(x - 3) + 1

y = (1/3)x - 1 + 1

y = (1/3)x

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Joe aura 35 pommes.

40-5=35

If the cost price of 20 articles is the same as selling price of 16 articles, then the gain percentage is 25%

To find the gain percent, we first need to calculate the profit earned on the sale of the 16 articles.

Let the cost price of each article be "C" and the selling price of each article be "S".

Given that the cost price of 20 articles is the same as the selling price of 16 articles, we can write:

20C = 16S

We can simplify this equation to:

S = (20/16)C = (5/4)C

Now, let's calculate the profit earned on the sale of 16 articles:

Profit = Total Selling Price - Total Cost Price

Profit = 16S - 20C

Profit = 16(5/4)C - 20C

Profit = 5C/2

The profit earned is 5C/2. The profit percent can be calculated as:

Profit Percent = (Profit / Cost Price) x 100

Profit Percent = (5C/2) / (20C) x 100

Profit Percent = 25%

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Meredith will take 8 hours 45 minutes to file 70% of the 10 reports given.

The time taken by Meredith to file 70% of the 10 reports given, given that each report takes an average of 75 minutes is 6 hours, 30 minutes. Therefore, the correct option is B. 6 hours, 30 minutes. How long will it take Meredith to file 70% of 10 reports, given that each report takes an average of 75 minutes to file?

Here, the total number of reports = 10

Average time to file one report = 75 minutes

To find out the time taken to file 70% of 10 reports, we will need to multiply the average time taken to file one report by the number of reports to be filed, which is 7 in this case:

75 × 7 = 525 minutes

We have calculated the time it will take Meredith to file 7 reports. Now, to convert this time to hours and minutes, we divide the total minutes by 60 to get the hours and then find out the remainder for the minutes:

525 ÷ 60 = 8 hours 45 minutes

Therefore, Meredith will take 8 hours 45 minutes to file 70% of the 10 reports given.

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The resulting double-line graph should show the sales data for desktop and laptop computers over the five days, with a line for each type of computer.

A double-line graph is a graph that displays two sets of data on the same graph, using two lines to show how each set of data changes over time or some other variable.

To create a double-line graph of the sales data for desktop and laptop computers over five days, follow these steps:

Draw a graph with two perpendicular axes, the horizontal axis (x-axis) representing the days, and the vertical axis (y-axis) representing the number of computers sold.

Label the horizontal axis with the days from Day 1 to Day 5.

Label the vertical axis with the heading "Number of Computers Sold".

Plot the data points for desktop computer sales. For Day 1, plot a point at (1, 4), for Day 2 plot a point at (2, 1), for Day 3 plot a point at (3, 2), for Day 4 plot a point at (4, 5), and for Day 5 plot a point at (5, 1).

Connect the data points for desktop computer sales with a line.

Plot the data points for laptop computer sales. For Day 1, plot a point at (1, 5), for Day 2 plot a point at (2, 2), for Day 3 plot a point at (3, 3), for Day 4 plot a point at (4, 7), and for Day 5 plot a point at (5, 3).

Connect the data points for laptop computer sales with a line.

Use a different color or style for the line representing desktop sales and the line representing laptop sales.

Add a legend to the graph to indicate which line corresponds to desktop sales and which corresponds to laptop sales.

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The average number of beads that the girls have is 63

Let's start by using algebra to represent the given information:

Let b be the number of beads that Sally has.

Then, Kelly has 3/4 times as many beads as Sally, which can be expressed as (3/4)b.

Also, we know that Kelly has 18 more beads than Sally, which can be expressed as (b + 18).

Putting these together, we can write the equation:

(3/4)b = b + 18

Solving for b, we get:

b = 72

So, Sally has 72 beads, and Kelly has (3/4) × 72 = 54 beads.

The average number of beads that the girls have is (72 + 54)/2 = 63 beads

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Answer: View answer in explanation below.

Step-by-step explanation: Let's use variables to represent the unknown quantities.

Let x be the number of $5 clearance mystery books purchased.

Let y be the number of $12 regular-priced science fiction books purchased.

We can set up a system of equations based on the given information:

5x + 12y = 126 (total amount spent)

x + y = total number of books purchased

We need to solve for x and y.

Let's use the second equation to solve for one variable in terms of the other:

y = total number of books purchased - x

Now we can substitute this expression for y into the first equation:

5x + 12(total number of books purchased - x) = 126

Simplifying and solving for x:

5x + 12total number of books purchased - 12x = 126

-7x + 12total number of books purchased = 126

-7x = -12total number of books purchased + 126

x = (12total number of books purchased - 126)/7

Since x must be a whole number (you can't buy a fraction of a book), we need to find a value of total number of books purchased that makes x a whole number. We can start by trying different values of total number of books purchased:

If total number of books purchased is 10:

x = (12(10) - 126)/7 = -6/7 (not a whole number)

If total number of books purchased is 11:

x = (12(11) - 126)/7 = 6/7 (not a whole number)

If total number of books purchased is 12:

x = (12(12) - 126)/7 = 6/7 (not a whole number)

If total number of books purchased is 13:

x = (12(13) - 126)/7 = 12/7 (not a whole number)

If total number of books purchased is 14:

x = (12(14) - 126)/7 = 18/7 (not a whole number)

If total number of books purchased is 15:

x = (12(15) - 126)/7 = 24/7 (not a whole number)

If total number of books purchased is 16:

x = (12(16) - 126)/7 = 30/7 (not a whole number)

If total number of books purchased is 17:

x = (12(17) - 126)/7 = 36/7 (not a whole number)

If total number of books purchased is 18:

x = (12(18) - 126)/7 = 42/7 = 6 (a whole number)

So, you bought 6 $5 clearance mystery books and 12 - 6 = 6 $12 regular-priced science fiction books.