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 separately fill a cistern in 10 and 15 minutes respectively. A person opens both the pipes together when the cistern should have been was full he finds the waste pipe open. He then closes the waste pipe and in another 4 minutes the cistern was full. In what time can the waste pipe empty the cistern when fill?

 Option A: 7

 Option B: 9

 Option C: 5

 Option D: 4

 Option E: 8
Option E

Question: Albert invested an amount of Rs. 8000 in a fixed deposit scheme for 2 years at compound interest rate 5 p.c.p.a. How much amount will Albert get on maturity of the fixed deposit?

 Option A: Rs. 8600

 Option B: Rs. 8620

 Option C: Rs. 8820

 Option D: Rs. 8000

 Option E: None of these
Option C

Question: How many different ways can you select a pilot and a co pilot if you have 70 people to choose from?

 Option A:  199

 Option B:  200

 Option C:  398

 Option D:  4830

 Option E:  9900

Option D