Another way: Any letter (x, y, z, w) can be included or not. So, we have 2^4 combinations - 4 empty combination = 12 combinations
From the set of numbers x, y, t, z, p, q, r and w, how many different combinations can we have without the t,p,q and r in them? Ex:. (x,y), (x), (w,z,y,x), etc and (x,y)=(y,x)
Options:
(A) 10
(B) 12
(C) 15
(D) 16
(E) 30
(B)

In 10s the train crosses the pole and in 35 sec the train crosses one more stationary train
In 25 sec the train travels a distance of 500 mtrs
Speed = 500/25 = 20 m/s = 20 (3600/1000) = 20 * 18/5 = 72 kmph
A Train requires 10 seconds to pass a pole while it requires 35 seconds to cross a stationary train which is 500 mtrs long. Find the speed of the train.
Options:
(A) 68 kmph
(B) 70 kmph
(C) 72 kmph
(D) 60 kmph
(E) 50 kmph
(C)

Speed = 60 * 5/18 = 50/3 m/sec
Length of the train = speed * time = 50/3 * 9 = 150 m
A train running at the speed of 60 km/hr crosses a pole in 9 sec. What is the length of the train?
Options:
(A) 118
(B) 150
(C) 277
(D) 258
(E) 191
(B)