10
QuizMultiple Choice

Using the Central Limit Theorem

Question 10 • CA-Statistics and Probability B

A course for a snail race has times that are skewed right with a mean of 5.18 minutes and a standard deviation of 2.34 minutes. If a random sample of 38 snails is selected, what is the probability that the mean race time is less than 4.3 minutes?

Answer
A
0.0102
B
0.3534
C
0.6466
D
0.9098

Explanation

For a sample of 38, the Central Limit Theorem lets us approximate the sample mean as normal. Its standard error is 2.34/√38 ≈ 0.380, so the z-score for 4.3 minutes is (4.3 − 5.18)/0.380 ≈ −2.32. The probability below this z-score is about 0.0102, so the answer is A, 0.0102.

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