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.

[EX Q]: Problem: a shop owner professes to sell his articles at certain cost price but he uses false weights with which he cheats by 12 % while buying and by 30 % while selling. what is his percentage profit ?
Options: a. 10.22 %, b. 20.22 %, c. 21.22 %, d. 60 %, e. ca n ' t be calculated
[EX A]: d

[EX Q]: Problem: the average of first six prime numbers greater than 20 is ?
Options: a. 10, b. 20, c. 30, d. 40, e. 34
[EX A]: e

[EX Q]: Problem: a box contains 100 pairs of shoes ( 200 shoes in total ). if two shoes are selected at random, what it is the probability that they are matching shoes ?
Options: a. 1 / 190, b. 1 / 20, c. 1 / 199, d. 1 / 10, e. 1 / 9
[EX A]:
c