Q: A and B together can do a work in 6 days. If A alone can do it in 15 days. In how many days can B alone do it?
Options:
(A) 7
(B) 13
(C) 19
(D) 10
(E) None
A: OK... Stream of consciousness: 1/6 1/15 = 1/10
B can do the work in 10 days
The answer is (D).

Q: A boy runs 200 metres in 60 seconds. What is his speed ?
Options:
(A) 12 km/hr
(B) 24 km/hr
(C) 13 km/hr
(D) 14 km/hr
(E) 16 km/hr
A: OK... Stream of consciousness: 200/60 * 18/5 = 12 km/hr
The answer is (A).

Q: Twenty coins are tossed simultaneously. In how many of the outcomes will the third coin turn up a head?
Options:
(A) 2^19
(B) 2^10
(C) 3 * 2^8
(D) 3 * 2^9
(E) 3 * 2^10
A: OK... Stream of consciousness: Fix the third coin as H. The remaining 19 coins have 2^19 outcomes.
The answer is (A).

Q: A man rows his boat 120 km downstream and 92 km upstream, taking 4 hours each time. Find the speed of the stream?
Options:
(A) 6 kmph
(B) 4 kmph
(C) 2 kmph
(D) 8 kmph
(E) 1 kmph
A:
OK... Stream of consciousness: Speed downstream = d/t = 120/(4) = 30 kmph
Speed upstream = d/t = 92/(4) = 23 kmph
The speed of the stream = (30 - 23)/2 = 4 kmph
The answer is (B).