# Chapter 7 Review.

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Chapter 7 Review

A z-score is: The mean of the distribution The deviation from the mean divided by the standard deviation Always positive The standard error

The mean score on a certain mathematics aptitude test is 72, with a standard deviation of Assume a normal distribution of scores. If a student's z-score on the test is known to have been at the 25th percentile, what was the student’s actual score? 66.267

The life of Sunshine Stereo CD players is normally distributed with a mean of 2.3 years and a standard deviation of 0.4 year. What proportion of the players will break during the guarantee period of 2 years? 0.2266

From the previous question, P(X < 2) = 0. 2266
From the previous question, P(X < 2) = If the store sells 10 of these CD players on a given day, what is the probability that at least 3 of the players will break during the guarantee period of 2 years? 0.4033

Suppose the average score on a national test is 500 with a standard deviation of If each score is increased by 25%, what are the new mean and standard deviation? m = 625 & s = 125

The mean score on a certain mathematics test is 72 with a standard deviation of Assume a normal distribution of scores. What score would one have to earn so that no more than 15% of the scores would be higher? 80.81

Suppose you toss a die with 3 red sides, 2 white sides, and 1 blue side. What is the probability that the first toss that lands blue is the 5th toss? .0804

In a recent study it was found that in one town the number of hours that a typical 10-year-old child watches television per week is evenly distributed with a median of 12 hours and a maximum of 15.5 hours. If Gary is a typical 10-year-old in this town, what is the probability that he watches between 9 and 14 hours? 0.7143

A traffic control engineer has found that the waiting time for a commuter in the Parker Road toll plaza of North Dallas Tollway during rush hour is approximately uniformly distributed with a mean of 8.7 minutes and a range of 5 minutes. What is the probability that the a randomly selected commuter will have to wait more than 10 minutes? 0.24

T F T Which of the following statements are true?
The area under a normal curve is always equal to 1, no matter what the mean and standard deviation are. The larger the standard deviation of a normal curve, the taller and thinner the curve. Normal curves with different means are centered around different numbers. T F T

A Cornell University researcher measured the mouth volumes of men and women. She found a mean of 66 cc for men (s = 17 cc) and a mean of 54 cc for women (s = 14.5 cc). If the distribution of mouth volumes is approximately normal, what is the probability that the difference in volumes (male – female) is at least 59 cc? .0179