Download 7.3 Assignment Solutions

7.3 Assignment
AP Statistics
The weights of newborn children in the United States vary according to the normal distribution with
mean 7.5 pounds and standard deviation 1.25 pounds. The government classifies a newborn as having
low birth weight if the weight is less than 5.5 pounds.
1. What is the probability that a baby chosen at random weighs less than 5.5 pounds at birth?
You choose three babies at random and compute their mean weight, x .
2. What are the mean and standard deviation of the mean weight x of the three babies?
3. What is the probability that their average birth weight is less than 5.5 pounds?
4. Would your answers to 1, 2, or 3 be affected if the distribution of birth weights in the population
were distinctly nonnormal?
The scores of students on the ACT college entrance examination in a recent year had the normal
distribution with mean µ = 20.4 and standard deviation σ = 5.8.
5. What is the probability that a randomly chosen student scored 24 or higher on the ACT?
6. What are the mean and standard deviation of the average ACT score x for an SRS of 30 students?
7. What is the probability that the average ACT score of an SRS of 30 students is 24 or higher?
8. Would your answers to 5, 6, or 7be affected if the distribution of ACT scores in the population was
distinctly nonnormal?