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: the purchase price of an article is $ 48. in order to include 5 % of cost for overhead and to provide $ 12 of net profit, the markup should be
Options: a. 15 %, b. 25 %, c. 30 %, d. 40 %, e. 45 %
[EX A]: c

[EX Q]: Problem: john can complete a given task in 18 days. jane will take only 12 days to complete the same task. john and jane set out to complete the task by beginning to work together. however, jane was indisposed 6 days before the work got over. in how many days did the work get over from the time john and jane started to work on it together ?
Options: a. 11, b. 34 / 5, c. 44 / 5, d. 54 / 5, e. 12
[EX A]: d

[EX Q]: Problem: what is the probability of randomly selecting one of the shortest diagonals from all the diagonals of a regular decagon ( 10 - sided polygon ) ?
Options: a. 3 / 10, b. 2 / 5, c. 2 / 7, d. 10 / 21, e. 5 / 11
[EX A]:
c