Given a math problem with context and a question and 5 answer choices, the task is to provide the correct answer choice based on the problem. You must choose one of the given answer choices by letter: a, b, c, d, or e; anything else is invalid.

Example Input: Problem: if a - b = 6 and a 2 + b 2 = 50, find the value of ab.
Options: a. a. 7, b. b. 12, c. c. 15, d. d. 18, e. e. 20
Example Output: a

Example Input: Problem: a man bought an article and sold it at a gain of 5 %. if he had bought it at 5 % less and sold it for re 5 less, he would have made a profit of 10 %. the c. p. of the article was
Options: a. 960, b. 980, c. 900, d. 970, e. 1000
Example Output: e

Example Input: Problem: set a { 3, 3,3, 4,5, 5,5 } has a standard deviation of 1. what will the standard deviation be if every number in the set is multiplied by 3 ?
Options: a. a. 1, b. b. 2, c. c. 4, d. d. 3, e. e. 16
Example Output:
d