q: If 1/2 of the air in a tank is removed with each stroke of a vacuum pump, what fraction of the original amount of air has been removed after 5 strokes ?
Options:
(A) 31/32
(B) 7/8
(C) 1/4
(D) 1/8
(E) 1/16
a: Stream of consciousness: Left After 1st stroke = 1/2
Left After 2nd stroke = 1/2 * 1/2 = 1/4
Left After 3rd stroke = 1/2 * 1/4 = 1/8
Left After 4th stroke = 1/2 * 1/8 = 1/16
Left After 5th stroke = 1/2 * 1/16 = 1/32
So removed = 1- 1/32 = 31/32 The answer is (A).

question: Ravi can do a piece of work in 25 days while Prakash can do it in 35 days. In how many days will they finish it together?
Options:
(A) 15 7/9 days
(B) 16 17/9 days
(C) 15 1/19 days
(D) 14 7/12 days
(E) 14 7/9 days
answer: Stream of consciousness: 1/25 + 1/35 = 12/175
175/12 = 14 7/12 days The answer is (D).

q: 10 books are placed at random in a shelf. The probability that a pair of books will always be together is -
Options:
(A) 1/5
(B) 1/3
(C) 1/4
(D) 118/2
(E) 21/4
a: Stream of consciousness: 10 books can be rearranged in 10! ways consider the two books taken as a pair then number of favourable ways of getting these two books together is 9! 2!
Required probability = 1/5 The answer is (C).

question: A 360 meter long train crosses a man standing on the platform in 6 sec. What is the speed of the train?
Options:
(A) 229
(B) 108
(C) 278
(D) 216
(E) 112
answer: Stream of consciousness: S = 360/6 * 18/5 = 216 kmph The answer is (D).

q: An analyst will recommend a combination of 3 industrial stocks, 2 transportation stocks, and 2 utility stocks. If the analyst can choose from 5 industrial stocks, 4 transportation stocks, and 4 utility stocks, how many different combinations of 7 stocks are possible?
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Options:
(A) 12
(B) 19
(C) 360
(D) 580
(E) 720
a: Stream of consciousness: 5C3 * 4C2 * 4C2 = 10*6*6 = 360. The answer is (C).

q: The average of 13 numbers is 59. Average of the first 7 of them is 57 and that of the last 7 is 61. Find the 8th number?
Options:
(A) 59
(B) 83
(C) 45
(D) 53
(E) 64
a:
Stream of consciousness: Sum of all the 13 numbers = 13 * 59 = 767
Sum of the first 7 of them = 7 * 57 = 399
Sum of the last 7 of them = 7 * 61 = 427
So, the 8th number = 427 + 399 - 767 = 59. The answer is (A).