Q: A pipe can fill a cistern in 18 minutes whereas the cistern when fill can be emptied by a leak in 20 minutes. When both pipes are opened, find when the cistern will be full?
Options:
(A) 17
(B) 180
(C) 70
(D) 120
(E) 12
A: OK... Stream of consciousness: 1/18 - 1/20 = 1/180
180 minutes
The answer is (B).

Q: The length of a rectangle is increased by 45% and its breadth is decreased by 20%. What is the effect on its area?
Options:
(A) 1288
(B) 1299
(C) 1000
(D) 10000
(E) 11600
A: OK... Stream of consciousness: 100 * 100 = 10000
145 * 80 = 11600
The answer is (E).

Q: he population of a city is 120,000. If it increases at the rate of 6% per annum, then what will be its population 2 years hence?
Options:
(A) 137787
(B) 134832
(C) 139776
(D) 139728
(E) 139718
A: OK... Stream of consciousness: Population after n years = P [1 + (R/100)]2
Population after 2 years = 120000 * [1 + 6/100]2 = (120000 x 53/50 x 53/50) = 134832
The answer is (B).

Q: 80 370 ? 1550 2440 3530
Options:
(A) 900
(B) 840
(C) 750
(D) 860
(E) 960
A:
OK... Stream of consciousness: 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 (D).