# AP Statistics Multiple-Choice Practice Questions: The Normal Distribution 2

### Test Information

9 questions

21 minutes

1. Assume the given distributions are normal. The average noise level in a restaurant is 30 decibels with a standard deviation of 4 decibels. Ninety-nine percent of the time it is below what value?

2. Assume the given distributions are normal. The mean income per household in a certain state is \$9500 with a standard deviation of \$1750. The middle 95% of incomes are between what two values?

3. Assume the given distributions are normal. One company produces movie trailers with mean 150 seconds and standard deviation 40 seconds, while a second company produces trailers with mean 120 seconds and standard deviation 30 seconds. What is the probability that two randomly selected trailers, one produced by each company, will combine to less than three minutes?

4. Assume the given distributions are normal. Jay Olshansky from the University of Chicago was quoted in Chance News as arguing that for the average life expectancy to reach 100, 18% of people would have to live to 120. What standard deviation is he assuming for this statement to make sense?

5. Assume the given distributions are normal. Cucumbers grown on a certain farm have weights with a standard deviation of 2 ounces. What is the mean weight if 85% of the cucumbers weigh less than 16 ounces?

6. Assume the given distributions are normal. If 75% of all families spend more than \$75 weekly for food, while 15% spend more than \$150, what is the mean weekly expenditure and what is the standard deviation?

7. Assume the given distributions are normal. A coffee machine can be adjusted to deliver any fixed number of ounces of coffee. If the machine has a standard deviation in delivery equal to 0.4 ounce, what should be the mean setting so that an 8-ounce cup will overflow only 0.5% of the time?

8. Assume that a baseball team has an average pitcher, that is, one whose probability of winning any decision is 0.5. If this pitcher has 30 decisions in a season, what is the probability that he will win at least 20 games?

9. Given that 10% of the nails made using a certain manufacturing process have a length less than 2.48 inches, while 5% have a length greater than 2.54 inches, what are the mean and standard deviation of the lengths of the nails? Assume that the lengths have a normal distribution.