Rationale: 1/20 + 1/30 - 1/40 = 7/120
120/7 = 17 1/7
The answer: (C)
Question: Two pipes A and B can fill a cistern in 20 and 30 minutes respectively, and a third pipe C can empty it in 40 minutes. How long will it take to fill the cistern if all the three are opened at the same time?
Options:
(A) 17 1/9
(B) 17 1/3
(C) 17 1/7
(D) 17 1/9
(E) 17 1/1

Rationale: Given Exp. = (a3 + b3) = (a + b) = (666 + 555) = 1221(a2 - ab + b2)
The answer: (D)
Question: Solve:-
666 x 666 x 666 + 555 x 555 x 555 = ?(666 x 666 - 666 x 555 + 555 x 555)
Options:
(A) 888
(B) 333
(C) 555
(D) 1221
(E) 889

Rationale: Speed = 36 * 5/18 = 10 m/sec
Total distance covered = 360 + 140 = 500 m
Required time = 500 * 1/10 = 50 sec
The answer: (B)
Question: A train 360 m long is running at a speed of 36 km/hr. In what time will it pass a bridge 140 m long?
Options:
(A) 40 sec
(B) 50 sec
(C) 88 sec
(D) 19 sec
(E) 10 sec