The average of 9 observations was 9, that of the 1st of 5 being 10 and that of the last 5 being 8. What was the 5th observation?
Options:
(A) 9
(B) 8
(C) 7
(D) 6
(E) 2

1 to 9 = 9 * 9 = 81
1 to 5 = 5 * 10 = 50
5 to 9 = 5 * 8 = 40
5th = 50 + 40 = 90 81 = 9 So the answer is: (A).

Find the C.I. on a sum of Rs.1600 for 9 months at 20% per annum, interest being compounded quarterly?
Options:
(A) 2266
(B) 7767
(C) 2522
(D) 1677
(E) 2671

A = 1600(21/20)3 = 2522 So the answer is: (C).

10 books are placed at random in a shelf. The probability that a pair of books will always be together is
Options:
(A) 1/6
(B) 1/9
(C) 1/5
(D) 1/6
(E) 1/3

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 So the answer is: (C).

Look at this series: F2, __, D8, C16, B32, ... What number should fill the blank?
Options:
(A) A16
(B) G4
(C) E4
(D) E3
(E) F2
Answer: Option C
The letters decrease by 1; the numbers are multiplied by 2. So the answer is: (C).