Rationale: 10 books can be rearranged in 10! ways consider the two books taken as a pair then number of favourable ways of getting these two books together is 9! 2!
Required probability = 1/5
The answer: (C)
Question: 10 books are placed at random in a shelf. The probability that a pair of books will always be together is
Options:
(A) 1/9
(B) 1/7
(C) 1/5
(D) 1/1
(E) 1/2


Rationale: (50/100) * 250 â€“ (25/100) * 400
125 - 100 = 25
The answer: (B)
Question: By how much is 50% of 250 greater than 25% of 400.
Options:
(A) 25
(B) 26
(C) 29
(D) 39
(E) 26


Rationale: Present age of total members = 6 X 26 = 156
10 yrs back their ages were = 6 x 10 = 60
Ages at the birth of youngest member = 156 - 60 = 96
Therefore, avg age at the birth of youngest member = 96/6 = 16.
The answer: (C)

Question: The average age of a family of 6 members is 26 years.If the age of the youngest member is 10 years,what was the average age of the family at the birth of the youngest member?
Options:
(A) 15
(B) 18
(C) 16
(D) 12
(E) 19