q: What is theleast number should be added to 1056, so the sum of the number is completely divisible by 23?
Options:
(A) 1
(B) 2
(C) 4
(D) 5
(E) 6
a: OK... (1056 / 23) gives remainder 21
21 + 2 = 23, So we need to add 2
The answer is (B).

q: 10 books are placed at random in a shelf. The probability that a pair of books will always be together i
Options:
(A) 1/6
(B) 1/0
(C) 1/5
(D) 1/2
(E) 1/1
a: OK... 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 is (C).

q: The average age of a class of 42 students is 16 yrs. if the teacher's age is also included, the average increases by one year. Find the age of the teacher
Options:
(A) 30 Years
(B) 31 Years
(C) 32 Years
(D) 34 Years
(E) 59 Years
a:
OK... Total age of students is 42X16 = 672 Years
Total age inclusive of teacher = 43X (16+1) = 731
So, Teacher's age is 731-672 = 59 Yrs
There is a shortcut for these type of problems
Teacher's age is 16+(43X1) = 59 Years
The answer is (E).