Find the mean proportional between 81 & 100?
Options:
(A) A) 59
(B) B) 61
(C) C) 63
(D) D) 65
(E) E) 90

Formula = ab
A = 81 and B = 100
81100 = 9 10 = 90 So the answer is: (E).

If six persons sit in a row, then the probability that three particular persons are always together is?
Options:
(A) 1/5
(B) 1/4
(C) 1/9
(D) 1/6
(E) 1/1

Six persons can be arranged in a row in 6! ways. Treat the three persons to sit together as one unit then there four persons and they can be arranged in 4! ways. Again three persons can be arranged among them selves in 3! ways. Favourable outcomes = 3!4! Required probability = 3!4!/6! = 1/5 So the answer is: (C).

A box contains 3 blue marbles, 4 red, 6 green marbles and 2 yellow marbles. If four marbles are picked at random, what is the probability that none is blue?
Options:
(A) 17/91
(B) 33/91
(C) 51/91
(D) 65/91
(E) None of these

Given that there are three blue marbles, four red marbles, six green marbles and two yellow marbles. When four marbles are picked at random, then the probability that none is blue is = C/C = (12 * 11 * 10 * 9)/(15 * 14 * 13 * 12) = 33/91 So the answer is: (B).

A 140 meter long train crosses a man standing on the platform in 6 sec. What is the speed of the train?
Options:
(A) 228
(B) 108
(C) 84
(D) 188
(E) 211
S = 140/6 * 18/5 = 84kmph So the answer is: (C).