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.

[EX Q]: Question: Two pipes A and B can fill a tank in 15 min and 20 min respectively. Both the pipes are opened together but after 4 min, pipe A is turned off. What is the total time required to fill the tank?

 Option A: 14 min 19 sec

 Option B: 14 min 42 sec

 Option C: 14 min 20 sec

 Option D: 14 min 40 sec

 Option E: 14 min 10 sec
[EX A]: Option D

[EX Q]: Question: If x and y are integers, what is the least positive number of 24x+18y?

 Option A: 3

 Option B: 6

 Option C: 9

 Option D: 12

 Option E: 15
[EX A]: Option B

[EX Q]: Question: If p/8 = r/2 and r = 0.75s, what is the ratio of p to r to s?

 Option A: 2 : 3 : 4

 Option B: 8 : 12 : 9

 Option C: 24 : 6 : 8

 Option D: 6 : 4 : 3

 Option E: 12 : 8 : 3
[EX A]:
Option C