Finding the wrong term

Example 1 :

Find out the wrong term from the following series and select the number from the alternatives which will replace the wrong term in the series.
299, 178, 97, 48, 24, 14, 13 :

(A) 175

(B) 295

(c) 23

(D) 10

Solution

We write the series in reverse order..And let us try with 23 instead of 24.So it becomes :

13 , 14 , 23 , 48 , 97 , 178 , 299

So difference between 2nd term and 1st term = 1

Between 3rd term and 2nd term = 9 = 32

Between 4th term and 3rd term = 25 = 52

Between 4th term and 3rd term = 49 = 72.

Hence the series now works fine..

Hence C) is the correct answer..

Example 2:

Find Out the Wrong Term in the Series 5, 15, 35, 77, 165, 221

Solution

Wrong numbers are 5 & 165.

The given pattern is in the form of:
3 * 5 = 15.
5 * 7 = 35.
7 * 11 = 77.
11 * 13 = 143.
13 * 17 = 221.

Therefore the wrong terms are 5 & 165.

Example 3: Find Out the Wrong Term in the Series

2,  3,  6,  15,  45,  156.5,  630

Solution:

Series pattern    Given Series

2                           2

2 × 1.5 = 3                 3

3 × 2 = 6                   6

6 × 2.5 = 15              15

15 × 3 = 45               45

45 × 3.5 = 157.5      156.5

157.5 × 4 = 630       630

Hence, there should be 157.5 in place of 156.5.

Example 4: Find Out the Wrong Term in the Series

36,  20,  12,  8,  6,  5.5,  4.5

Solution: 

The series is –16, –8, –4, –2, –1, –0.5, and so on.

Series pattern    Given Series

36                          36

36 – 16 = 20                  20

20 – 8 = 12                     12

12 – 4 = 8                         8

8 – 2 = 6                           6

6 – 1 = 5                         5.5

5 – 0.5 = 4.5                  4.5

Hence, there should be 5 in place of 5.5.

Example 5: Find Out the Wrong Term in the Series

1,  3,  9,  31,  128,  651,  3913

Solution:

Series pattern    Given Series

1                             1

1 × 1 + 2 = 3                   3

3 × 2 + 3 = 9                  9

9 × 3 + 4 = 31                31

31 × 4 + 5 = 129            128

129 × 5 + 6 = 651           651

651 × 6 + 7 = 3913       3913

Hence, there should be 129 in place of 128.