You are given a math word problem and you are supposed to make use of mathematical concepts like probability, combinatorics, linear equations, sequences/series, or simple operators like addition, subtraction, division, or multiplication to answer the given question. Choose the best option from the 5 given options and report that option.

[Q]: Question: A boy and a girl appear for an interview against 2 vacant posts in an office. The probability of the boy's selection is 1/5 and that of the girl's selection is 1/3. What is the probability that only 1 of them is selected?

 Option A: 1/3

 Option B: 2/5

 Option C: 3/5

 Option D: 4/7

 Option E: 5/9
[A]: Option B


[Q]: Question: If j and k are integers whose product is 400, which of the following statements must be true?

 Option A: n + k > 0

 Option B: n is not equal to k.

 Option C: Either n or k is a multiple of 10.

 Option D: If n is even, then k is odd.

 Option E: If j is odd, then k is even.
[A]: Option E


[Q]: Question: A man buys an article for $100. and sells it for $120. Find the gain percent?

 Option A: 10%

 Option B: 15%

 Option C: 25%

 Option D: 20%

 Option E: 30%
[A]:
Option D