Quantitative Aptitude - Arithmetic Ability Questions

The given number series is 90 72 56 42 36 20

9 x 10 = 90

8 x 9 = 72

7 x 8 = 56

6 x 7 = 42

5 x 6 = 30 (not 36) 

4 x 5 = 20

Hence, the odd man in the given number series is 36.

The only even numbers in the list are 2 and 4, but 4 is not a prime. So 2 can be used to illustrate the statement that all primes are not odd.

The given number series is 14, 27, 105, 525, 4993

14

14 x 2 - 1 = 27

27 x 4 - 3 = 105

105 x 6 - 5 = 625 (not 525)

625 x 8 - 7 = 4993

Hence, the odd man or number in the given number series is 525.

The given number series is 120, 36, 6, 2, 1, 1

120

120/5 = 24 (not 36)

24/4 = 6

6/3 = 2

2/2 = 1

1/1 = 1

Hence, the odd man in the given number series is 24.

Let the required numbers be x, 2x, 3x.   Then, their H.C.F =x. so, x= 12

Therefore, The numbers are 12, 24, 36

The given number series is 10, 21, 54, 109, 189

The series follows a pattern that

10 + 11 = 21

21 + 33 = 54

54 + 55 = 109

109 + 77 = 186

Hence the wrong number in the given number series is 189.