Question: Two pipes A and B can fill a cistern in 8 and 12 minutes respectively, and a third pipe C can empty it in 15 minutes. How long will it take to fill the cistern if all the three are opened at the same time?
Options:
(A) 17 1/17 min
(B) 28 1/7 min
(C) 17 1/7 min
(D) 17 1/8 min
(E) 17 5/7 min
Answer: 1/8 + 1/12 - 1/15 = 17/120
120/17 = 7 1/17
The answer is (A).

Question: 10, 14, 16, 18, 21, 24, 26
Options:
(A) 17
(B) 20
(C) 21
(D) 25
(E) 26
Answer: Each of the numbers except 21 is an even number
The answer is (C).

Question: How much 60% of 50 is greater than 30% of 30?
Options:
(A) 21
(B) 91
(C) 11
(D) 17
(E) 12
Answer: (60/100) * 50 (30/100) * 30
30 - 9 = 21
The answer is (A).

Question: 80 370 860 1550 2440 ?
Options:
(A) 900
(B) 840
(C) 750
(D) 860
(E) 3530
Answer:
10^2 - 20 = 80
20^2 - 30 = 370
30^2 - 40 = 860
40^2 - 50 = 1550
50^2 - 60 = 2440
60^2 - 70 = 3530.
The answer is (E).