Scores on the ACT college entrance exam follow a bell-shaped distribution with a mean 18 and a standard deviation 6. Wayne’s standardized score on the ACT was 0.7 What was Wayne’s actual ACT score? (a)4.2(b)4.2(c)13.8(d)17.3(e)22.2

Short Answer

Expert verified

The correct option is (c).

Step by step solution

01

Step 1. Given

The average population (μ)=18

The standard deviation of the population (σ)=6

A score that is standardized (z)=-0.7

02

Step 2. Concept

The z score is calculated using the following formula: z=Xμ/σ

03

Step 3. Calculation

Consider that X reflects Wayne's real ACT score, which follows a normal distribution with a mean of 18and a standard deviation of6.

Wayne's real ACT score is determined as follows:

z=Xμσ

0.7=X186

4.2+18=X

X=13.8

Hence, the correct option is (c)13.8

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Most popular questions from this chapter

Paul is15years old and 179cm tall.

(a) Find the z-score corresponding to Paul’s height. Explain what this value means.

(b) Paul’s height puts him at the85th percentile among 15-year-old males. Explain what this means to someone who knows no statistics.

Teacher raises A school system employs teachers at salaries between \(28,000 and \)60,000. The teachers’ union and the school board are negotiating the form of next year’s increase in the salary schedule.

(a) If every teacher is given a flat \(1000 raise, what will this do to the mean salary? To the median salary? Explain your answers.

(b) What would a flat\)1000 raise do to the extremes and quartiles of the salary distribution? To the standard deviation of teachers’ salaries? Explain your answers.

Use Table A to find the value zfrom the standard Normal distribution that satisfies each of the following conditions. In each case, sketch a standard Normal curve with your value of zmarked on the axis. Use your calculator or the Normal Curve applet to check your answers.

Working backward

(a) The 10th percentile.

(b) 34% of all observations are greater thanz.

Shoes How many pairs of shoes do students have? Do girls have more shoes than boys? Here are data from a random sample of 20 female and 20 male students at a large high school:

(a) Find and interpret the percentile in the female distribution for the girl with 22pairs of shoes.

(b) Find and interpret the percentile in the male distribution for the boy with 22 pairs of shoes.

(c) Who is more unusual: the girl with22 pairs of shoes or the boy with 22 pairs of shoes? Explain.

Use Table A in the back of the book to find the proportion of observations from a standard Normal distribution that fall in each of the following regions. In each case, sketch a standard Normal curve and shade the area representing the region.

3.0.56<z<1.81

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