question: There are 15 balls in a jar. You take out 3 blue balls without putting them back inside, and now the probability of pulling out a blue ball is 1/3. How many blue balls were there in the beginning?
Options:
(A) 12.
(B) 9.
(C) 8.
(D) 7.
(E) 6.
answer: Stream of consciousness: 7 = 3 blue balls + 12 / 3 The answer is (D).
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question: 10 books are placed at random in a shelf. The probability that a pair of books will always be together is?
Options:
(A) 1/0
(B) 1/3
(C) 1/5
(D) 1/2
(E) 1/1
answer: 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).
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question: n what time will a railway train 60 m long moving at the rate of 36 kmph pass a telegraph post on its way?
Options:
(A) 2
(B) 7
(C) 8
(D) 6
(E) 9
answer: Stream of consciousness: T = 60/36 * 18/5 = 6 sec The answer is (D).
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question: The average of 9 results is 50. The average of first four results is 52 and average of last four results is 49 . what is the fifth result?
Options:
(A) 22
(B) 27
(C) 29
(D) 46
(E) 92
answer:
Stream of consciousness: Total of results = 50 x 9 = 450
Total of first four results = 52 x 4 = 208
Total of Last four results = 49 x 4 = 196
Hence the fifth result = 450 - (208 + 196) = 46 The answer is (D).
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