Bunuel wrote:

If Set A is made up of all 2-digit primes that are one less than a power of 2, what is the standard deviation of set A?

A. 0

B. 15.1

C. 17

D. 20

E. 23.7

The only 2-digit powers of 2 are:

16, 32, 64

If we subtract one from each of these numbers, we have:

15, 31, 63

Since the only prime number is 31, set A = {31}. Lastly, since there is only 1 number in the set, the standard deviation is zero.

Answer: A

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