Question

The number of books borrowed from a library each week follows a normal distribution. When a sample is taken for several weeks, the mean is found to be 190 and the standard deviation is 30. What is the percentage of the chance that more than 250 books were borrowed in a week?

a. 99.7
b. 95
c. 13.5
d. 2.5

Answer 1

D. 2.5

Explanation:

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Answer 2

1 SD away from mean is 68% of data.
2 SD away from mean is 95% of data.
3 SD away from mean is 99.7% of data.

1 SD away:
190+30=220

2 SD away:
220+30=250

This shows we are on the outer 5 percent of the normal distribution.
Since you said "more", that means we only look at the right side of your 5%, which is only 2.5%

answer is D, 2.5%