Series questions in reasoning are basically of two types, Series completion (missing term, next term) and Series correction (finding the wrong element in the series).

**Question 1 : ** Find the missing term : 157.5, 45, 15, _, 3, 2, 2

**Solution : ** Le the missing number be ‘n’

157.5 / 45 = 3.5

45 / 15 = 3

15 / n = 2.5

n / 3 = 2

3 / 2 = 1.5

2 / 2 = 1

Therefore, the missing number is 6.

**Question 2 : ** Find the next term in the series : 6, 7, 9, 13, _

**Solution : ** Let the missing number be ‘n’

7 – 6 = 1

9 – 7 = 2

13 – 9 = 4

n – 13 = 8

Therefore, next number in the series = n = 21

**Question 3 : ** Find the incorrect element in the series : 1, 3, 10, 36, 152, 760, 4632

**Solution : **

1 x 1 + 2 = 3

3 x 2 + 4 = 10

10 x 3 + 6 = 36

36 x 4 + 8 = 152

152 x 5 + 10 = 770

770 x 6 + 12 = 4632

Therefore, the incorrect element in the series is 760.

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