Question: A can do a piece of work in 3 hours; B and C together can do it in 2 hours, which A and B together can do it in 2 hours. How long will C alone take to do it?
Options:
(A) 2hours
(B) 5hours
(C) 6hours
(D) 4hours
(E) 3hours
Answer: A's 1 hour work = 1/3;
(B + C)'s 1 hour work = 1/2;
(A + B)'s 1 hour work = 1/2
(A + B + C)'s 1 hour work = (1/3 + 1/2) = 5/6
C's 1 hour work = (5/6 - 1/2) = 1/3
C alone will take 3 hours to do the work.
The answer is (E).

Question: The average of 11 results is 50, if the average of first six results is 49 and that of the last six is 52. Find the sixth result?
Options:
(A) 22
(B) 56
(C) 88
(D) 66
(E) 21
Answer: 1 to 11 = 11 * 50 = 550
1 to 6 = 6 * 49 = 294
6 to 11 = 6 * 52 = 312
6th = 294 + 312 550 = 56'
The answer is (B).

Question: A pipe can fill a cistern in 20 minutes whereas the cistern when fill can be emptied by a leak in 28 minutes. When both pipes are opened, find when the cistern will be full?
Options:
(A) 76 minutes
(B) 29 minutes
(C) 70 minutes
(D) 17 minutes
(E) 98 minutes
Answer: 1/20 - 1/28 = 1/70
70 minutes
The answer is (C).

Question: A train 250 m long running at 72 kmph crosses a platform in 15 sec. What is the length of the platform?
Options:
(A) 50m
(B) 200m
(C) 250m
(D) 270m
(E) 300 m
Answer:
D = 72 * 5/18 = 15 = 300 250 = 50m
The answer is (A).