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: what is the value of n if the sum of the consecutive odd intergers r from 1 to n equals 169 ?
Options: a. 47, b. 25, c. 37, d. 33, e. 29
[EX A]: b

[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: two tains of equal lengths take 10 seconds and 15 seconds respectively to cross a telegraph post. if the length of each train be 120 metres, in what time ( in seconds ) will they cross each other travelling in opposite direction ?
Options: a. 12, b. 14, c. 16, d. 20, e. 18
[EX A]:
a