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.

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
Option C

Question: X is a prime number bigger than 10. Also, Y = X+X^3+X^5+X^7. What is definitely true about Y?

Option A: Y is a prime number.

Option B: Y is odd.

Option C: Y is even.

Option D: Y is divisible by 3.

Option E: Y is divisible by 7.
Option C

Question: The average (arithmetic mean) of 7, 8, 10 and 11 equals the average of 2, 9, 13, and

Option A: 7

Option B: 9

Option C: 10

Option D: 12

Option E: 13
Option D