Q: A can do a piece of work in 9 days. When he had worked for 2 days B joins him. If the complete work was finished in 8 days. In how many days B alone can finish the work?
Options:
(A) 18
(B) 77
(C) 66
(D) 54
(E) 12
A: OK... Stream of consciousness: 8/9 + 6/x = 1
X = 54 days
The answer is (D).

Q: 80 white and black tiles will be used to form a 10x10 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) 80
(C) 85
(D) 90
(E) 60
A: OK... Stream of consciousness: Answer = E
Please refer diagram below
70 - 10 = 60
The answer is (E).

Q: A train 455 m long, running with a speed of 63 km/hr will pass a tree in?
Options:
(A) 22 sec
(B) 16 sec
(C) 17 sec
(D) 39 sec
(E) 12 sec
A: OK... Stream of consciousness: Speed = 63 * 5/18 = 35/2 m/sec
Time taken = 455 * 2/35 = 39 sec
The answer is (D).

Q: If six persons sit in a row, then the probability that three particular persons are always together is?
Options:
(A) 1/5
(B) 1/4
(C) 1/9
(D) 1/6
(E) 1/1
A:

Show your work and conclude with the exact phrasing "Therefore, the final answer is [answer]." where [answer] is just the final number or expression that solves the problem.
user
OK... 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
The answer is (C).