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 man can do a piece of work in 5 days, but with the help of his son he can do it in 3 days. In what time can the son do it alone ?

 Option A: 13/2

 Option B: 19/2

 Option C: 21/2

 Option D: 15/2

 Option E: None
[A]: Option C


[Q]: Question: There are 4 boys and 3 girls seated in a row.Find the probability that all girls are together?

 Option A: 1/6

 Option B: 1/7

 Option C: 2/7

 Option D: 3/7

 Option E: 4/7
[A]: Option B


[Q]: Question: The Natural Woman, a women's health food store, offers its own blends of trail mix. If the store uses 4 different ingredients, how many bins will it need to hold every possible blend, assuming that each blend must have at least two ingredients? (Also assume that each bin can hold one and only one blend.)

 Option A: 1

 Option B: 4

 Option C: 7

 Option D: 11

 Option E: 10
[A]:
Option D