8^10 = (2^3)^10 = 2^30
What is the greatest positive integer x such that 2^x is a factor of 8^10?
Options:
(A) 5
(B) 9
(C) 10
(D) 20
(E) 30
(E)

D = 60 * 5/18 = 35 = 583 120 = 463
A train 120 m long running at 60 kmph crosses a platform in 35 sec. What is the length of the platform?
Options:
(A) 338
(B) 277
(C) 463
(D) 456
(E) 271
(C)

1/20 + 1/30 - 1/40 = 7/120
120/7 = 17 1/7
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) 19 1/7 min
(B) 15 1/7 min
(C) 17 1/7 min
(D) 7 1/7 min
(E) 7 2/7 min
(C)