instruction:
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.
question:
Problem: a man ' s speed with the current is 18 km / hr and the speed of the current is 2.5 km / hr. the man ' s speed against the current is ?
Options: a. 10, b. 18, c. 50, d. 30, e. 40
answer:
b

question:
Problem: the least number which when divided by 5, 6, 7 and 8 leaves a remainder 3, but when divided by 9 leaves no remainder, is :
Options: a. 2377, b. 1683, c. 2677, d. 9972, e. 1611
answer:
b

question:
Problem: the age of somu is one - third his father ' s. 7 years back he was one - fifth of his father ' s age. what is his persent age ?
Options: a. 11, b. 13, c. 14, d. 12, e. 10
answer:
c