q: A train 490 m long, running with a speed of 63 km/hr will pass a tree in?
Options:
(A) 18 sec
(B) 16 sec
(C) 76 sec
(D) 15 sec
(E) 28 sec
a: OK... Speed = 63 * 5/18 = 35/2 m/sec
Time taken = 490 * 2/35 = 28 sec
The answer is (E).

q: The average of 10 numbers is calculated as 15. It is discovered later on that while calculating the average, one number namely 36 was wrongly read as 26. The correct average is?
Options:
(A) 22
(B) 88
(C) 16
(D) 83
(E) 82
a: OK... 10 * 15 + 36 – 26 = 160/10 = 16
The answer is (C).

q: A and B can do a work in 10 days and 15 days respectively. A starts the work and B joins him after 2 days. In how many days can they complete the remaining work?
Options:
(A) 6 days
(B) 2 days
(C) 4 4/5 days
(D) 3 days
(E) 9 days
a:
OK... Work done by A in 2 days = 2/10 = 1/5
Remaining work = 4/5
Work done by both A and B in one day = 1/10 + 1/15 = 5/30 = 1/6
Remaining work = 4/5 * 6/1 = 24/5 = 4 4/5 days.
The answer is (C).