The amount of time spent by American adults watching TV per day is normally dist
ID: 2506556 • Letter: T
Question
The amount of time spent by American adults watching TV per day is normally distributed
with a mean of 6 hours and a standard deviation of 1.5 hours.
a. What is the probability that a randomly selected American adult watches television for more than 7
hours per day?
b. What is the probability that the average time spent watching TV in a random sample of 5 American
adults is more than 7 hours?
c. What is the probability that the average time spent watching TV in a random sample of 30 American adults is more than 7 hours?
Explanation / Answer
a) z-score = 1/1.5 = .666. Looking up on the table, the probability is about 0.7486.
b) The standard error is the standard deviation divided by the square root of the sample size, or 1.5 / sqrt (5). The z-score is 1/(1.5/sqrt(5)), or about 1.49. Looking up on the table, the probability is about 0.9319.
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