Help me please!

Question

I really do not understand this.

If anyone can help me, that would be great:

Five random books are chosen from a library shelf. The books have the following number of pages: {546, 434, 601, 498, 580}. Compared to these books, what would be a book that has an abnormally large number of pages?

Group of answer choices:

657

660

623

Both A and B

I really don't understand this! Any help would be greatly appreciated!

Answer 1

sum the given 5 numbers, divide by 5 and that = the mean = 531.8

standard deviation =square root of the sum of (squared differences from the mean divided by 5 or 4) depending on whether the data are the population or just a sample of the population

s =about 67.12

of the 3 possible answers 658, 660, 623

658 = 531.8+ 126.2. 126.2/67.12 = 1.88 standard deviations from the mean

660 = 531.8 + 128.2, 128.2/67.12 = 1.91 standard deviations from the mean

623 = 531.8 + 91.2, 91.2/67.12 = 1.36 standard deviations from the mean

"Normally" anything more than 2 standard deviations would be considered "abnormal"

as it's beyond the 95% confidence interval

but none of the above is not an option in this problem

Go with both A and B. Round A or B to nearest integer z score, they're both 2

a strange question, what's not "normal" but the above might make some sense out of it

possibly the instructor or textbook writer had more info that makes more sense of the problem