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 cistern in 20 and 30 minutes respectively, and a third pipe C can empty it in 40 minutes. How long will it take to fill the cistern if all the three are opened at the same time?

 Option A: 17 1/5

 Option B: 17 1/8

 Option C: 17 1/7

 Option D: 17 1/1

 Option E: 17 1/2
[EX A]: Option C

[EX Q]: Question: A certain population of bacteria doubles every 10 minutes. If the number of bacteria in the population initially was 10^5, then what was the number in the population 50 minutes later?

 Option A: 2(10^5

 Option B: 5(10^5

 Option C: (2^5

 Option D: (10^5

 Option E: (10^5
[EX A]: Option C

[EX Q]: Question: If a person walks at 14 km/hr instead of 10 km/hr, he would have walked 20 km more. The actual distance travelled by him is:

 Option A: 50 Km

 Option B: 55 Km

 Option C: 45 Km

 Option D: 35 Km

 Option E: 40 Km
[EX A]:
Option A