q: There are 8 books in a shelf that consist of 1 paperback books and 7 hardback books. If 4 books are selected at random without replacement, how many different combinations are there that at least one paperback book is selected?
Options:
(A) 35
(B) 45
(C) 50
(D) 55
(E) 60
a: OK... 8C4 [Select any four] - 7C4 [Select all hard backs] = 35.
The answer is (A).

q: 100 white and black tiles will be used to form a 20x20 square pattern. If there must be at least one black tile in every row and at least one white tile in every column, what is the maximum difference between the number of black and white tiles that can be used?
Options:
(A) 75
(B) 70
(C) 85
(D) 90
(E) 95
a: OK... Answer = B
Please refer diagram below
90 - 20 = 70
The answer is (B).

q: Find the wrong number below mentioned series
3,20,50,60,80
Options:
(A) 80
(B) 60
(C) 50
(D) 20
(E) 3
a:
OK... 3 is the only prime number or odd number in the series.
The answer is (E).