question:A pipe can fill a cistern in 20 minutes whereas the cistern when fill can be emptied by a leak in 45 minutes. When both pipes are opened, find when the cistern will be full?
Options:
(A) 17 minutes
(B) 87 minutes
(C) 36 minutes
(D) 27 minutes
(E) 11 minutes
answer:(C)
Stream of consciousness:1/20 - 1/45 = 1/36
36 minutes

question:Look at this series: 201, 202, 204, 207, ... What number should come next?
Options:
(A) 211
(B) 205
(C) 224
(D) 267
(E) 269
answer:(A)
Stream of consciousness:In this addition series, 1 is added to the first number; 2 is added to the second number; 3 is added to the third number; 4 is added to the fourth number; and go on.

question:Let the second number be 3x, so that the first number is 6x and the third number is 2x.
Options:
(A) 22
(B) 77
(C) 98
(D) 27
(E) 36
answer:
(E)
Stream of consciousness: 6x + 3x + 2x = 132 x = 12. Second number = 3x = 312 = 36.