Wrong Number Series

A number series is a grouping of numbers that follow a certain logic or a mathematical formula. In IBPS PO, SO, SBI Clerk, SBI SO exams the questions on Wrong Number Series are very frequent. They are mostly present in the quantitative section and have a few types of questions.Here we will discuss all kinds of number series questions that can fall under the section on Quantitative Aptitude.

Directions (Q. 1-10): In each of these questions a number series is given. In each series only one number is wrong. Find out the wrong number.

1).  50, 51, 47 ,56 ,42 ,65, 29

A.51                B.47                C.56                D.42                E.65

Solution: The series is 50 + 1^2 = 51, 51 – 2^2 = 47, 47 + 3^2 = 56, 56 – 4^2 = 40, 40 + 5^2 = 65, 65 – 6^2 = 29.

Hence, there should be 40 in place of 42.

2).  3 ,9, 23, 99 ,479, 2881 ,20159

A.9                  B.23                C.99                D.479              E.2881

Solution: The series is 3 × 2 + 3 = 9, 9 × 3 – 4 = 23, 23 × 4 + 5 = 97, 97 × 5 – 6 = 479, 479 × 6 + 7 = 2881, 2881 × 7 – 8 = 20159

Hence, there should be 97 in place of 99.

3).  7 ,4 ,6, 9, 20, 52.5 ,160.5

A.6                  B.4                  C.20                D.9                  E.5

Solution: The series is x0.5 + 0.5, x1 + 1, x 1.5 + 1.5, x 2 + 2, x 2.5 + 2.5, x 3 + 3…

Hence, there should be 5 in place of 6.

4).  1, 3 ,6 ,11 ,20 ,39 ,70

A.3                  B.39                C.11                D.20                E.6

Solution: The series is 1 × 2 + 1 = 3, 3 × 2 + 0 = 6, 6 × 2 – 1 = 11, 11 × 2 – 2 = 20, 20 × 2 – 3 = 37, 37 × 2 – 4 = 70.

Hence, there should be 37 in place of 39.

5).  2, 13, 27 ,113 ,561 ,3369 ,23581

A.27                B.13                C.113              D.561              E.3369

Solution: The series is 2 × 2 + 7 = 11, 11 × 3 – 6 = 27, 27 × 4 + 5, = 113, 113 × 5 – 4 = 561, 561 × 6 + 3 = 3369, 3369 × 7 – 2 = 23581.

Hence, there should be 11 in place of 13.

6). 7 ,16 ,27, 40, 46

A.7                  B.16                C.27                D.40                E.46

The series is 5 × 1 + 2 = 7, 6 × 2 + 4 = 16, 7 × 3 + 6 = 27, 8 × 4 + 8 = 40, 9 × 5 + 10 = 55.

Hence, there should be 55 in place of 46.

Alternate Method: +9, +11, +13, +15

7). 729 ,1331 ,2497 ,3375, 4913

A.729              B.1331                        C.3375                        D.2497                        E.4913

The series is 9^3, 11^3, 13^3, 15^3, 17^3,

Hence, there should be 2197 in place of 2497.

8). 80, 119, 166 ,221 ,223

A.80                B.119              C.166              D.192              E.223

The series is 9^2 – 1, 11^2 – 2, 13^2 – 3, 15^2 – 4, 17^2 – 5,

Hence, there should be 284 in place of 223.

9). 8 ,8.5, 11.5 ,14 ,17

A.8                  B.8.5               C.11.5             D.14                E.17

The series is 8 + 1.5 = 9.5, 9.5 + 2 = 11.5, 11.5 + 2.5 = 14, 14 + 3 = 17

Hence, there should be 9.5 in place of 8.5.

10). 439, 778, 1456, 2812, 5624

A.439              B.778              C.1456                        D.2812                        E.5624

The series is +339, +678, +1356, +2712,

Hence, there should be 5524 in place of 5624.