question: If we need to change the average age of a group containing 4 persons from 40 to 38 by adding a person. What should be the age of the person newly added to the group?
Options:
(A) 20
(B) 25
(C) 30
(D) 38
(E) 40
answer: Stream of consciousness: Sum of the ages of the group having 4 persons and average 40 = 4x40 = 160
Sum of the ages of the group having 5 persons and average 38 = 5x38 = 190
Age of the new person added to the group = 190-160 = 30 The answer is (C).
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question: What is the are of an equilateral triangle of side 18 cm?
Options:
(A) 663 cm2
(B) 743 cm2
(C) 813 cm2
(D) 645 cm2
(E) 143 cm2
answer: Stream of consciousness: Area of an equilateral triangle = 3/4 S2
If S = 18, Area of triangle = 3/4 * 18 * 18 = 813 cm2; The answer is (C).
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question: 100 white and black tiles will be used to form a 20x20 square pattern. If there must be at least one black tile in every row and at least one white tile in every column, what is the maximum difference between the number of black and white tiles that can be used?
Options:
(A) 75
(B) 70
(C) 85
(D) 90
(E) 95
answer: Stream of consciousness: Answer = B
Please refer diagram below
90 - 20 = 70 The answer is (B).
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question: he population of a city is 130,000. If it increases at the rate of 6% per annum, then what will be its population 2 years hence?
Options:
(A) 146069
(B) 146067
(C) 156068
(D) 146068
(E) 179718
answer:
Stream of consciousness: Population after n years = P [1 + (R/100)]2
Population after 2 years = 130000 * [1 + 6/100]2 = (130000 x 53/50 x 53/50) = 146068 The answer is (D).
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