question:If 1/2 of the air in a tank is removed with each stroke of a vacuum pump, what fraction of the original amount of air has been removed after 6 strokes ?
Options:
(A) 63/64
(B) 7/8
(C) 1/4
(D) 1/8
(E) 1/16
answer:(A)
Stream of consciousness:Left After 1st stroke = 1/2
Left After 2nd stroke = 1/2 * 1/2 = 1/4
Left After 3rd stroke = 1/2 * 1/4 = 1/8
Left After 4th stroke = 1/2 * 1/8 = 1/16
Left After 5th stroke = 1/2 * 1/16 = 1/32
Left After 6th stroke = 1/2 * 1/32 = 1/64
So removed = 1- 1/64 = 63/64

question:What is the greatest positive integer x such that 7^x is a factor of 343^10?
Options:
(A) 5
(B) 9
(C) 10
(D) 20
(E) 30
answer:(E)
Stream of consciousness:343^10 = (7^3)^10 = 7^30

question:There are 11 person among whom 2 are brother. The total no.of ways in which these persons can be seated around a round table so that exactly 1 person sit between the brothers, is equal to?
Options:
(A) 4!*2!
(B) 7!*2!
(C) 6!*1!
(D) 2!*1!
(E) 8!*2!
answer:
(E)
Stream of consciousness:Total number of ways = 8!*2!.