q: (y^n - b^n) is completely divisible by (y - b), when
Options:
(A) n is odd natural number
(B) n is even natural number
(C) n is any natural number
(D) n is prime
(E) None
a: Stream of consciousness: For every natural number n, (y^n - b^n) is completely divisible by (y - b). The answer is (C).
--
q: The average of 13 numbers is 60. Average of the first 7 of them is 57 and that of the last 7 is 61. Find the 8th number?
Options:
(A) 46
(B) 83
(C) 45
(D) 53
(E) 64
a: Stream of consciousness: Sum of all the 13 numbers = 13 * 60 = 780
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 - 780 = 46. The answer is (A).
--
q: If six persons sit in a row, then the probability that three particular persons are always together is -.
Options:
(A) 1/5
(B) 1/7
(C) 1/9
(D) 1/2
(E) 2/7
a:
Stream of consciousness: 3!4! Required probability = 3!4!/6! = 1/5 The answer is (A).
--