If six persons sit in a row, then the probability that three particular persons are always together is ?
Options:
(A) 1/6
(B) 1/0
(C) 1/5
(D) 1/4
(E) 1/1
Answer and stream of consciousness: (C)
Stream of consciousness: 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

A owner of a mart earns an income of Re 1 on the first day of his business. On every subsequent day, he earns an income which is just double of that made on the previous day. On the 10th day of business, he earns an income of:
Options:
(A) 18
(B) 21
(C) 22
(D) 20
(E) 30
Answer and stream of consciousness: (A)
Stream of consciousness: 2nd day he earns = 2(2 1)
3rd day he earns = 2(3 1)
On 10th day he earns 2(10 -1) = 18 rupees

In a family, the father took 1/4 of the cake and he had 3 times as much as each of the other members had. The total number of family members is
Options:
(A) 3
(B) 7
(C) 10
(D) 12
(E) 15
Answer and stream of consciousness: (C)
Stream of consciousness: 1-1/4 = remain cake 3/4
3/4*3 = 9/4
9/4+1/4 = 10

A sum of money doubles itself at a compound interest in 15 years . In how may years it will become 8 times ??
Options:
(A) 30 years
(B) 40 years
(C) 45 years
(D) 50 years
(E) 60 years
Answer and stream of consciousness:
(C)
Stream of consciousness: If the sum doubles (x2) in 15 years, then it to become 2*2*2 = 8 times as large it should double three times, so three 15 years time period are needed, which is 3*15 = 45 years.