Jun 122012

What will come next in the below number series:

A) 4, 6, 12, 18, 30, 42, 60, 72, ? B) 22, 21, 23, 22, 24, 23, ?, ? C) 5, 6, 7, 8, 10, 11, 14, ?, ?

### Solution:

Let me confess that Questions related to number series are not asked very frequently in companies. Only few companies have such questions in their written test (for professionals with 0-2 years of experience).

Having said that, lets have a look at the questions above:

**A) Answer: 102**

This series represents average of twin prime numbers (Prime numbers whose difference is just 2).

4 = (3+5)/2 6 = (5+7)/2 12 = (11+13)/2 18 = (17+19)/2 30 = (29+31)/2 ...

So the next three number in the series will be (101 + 103)/2 = 102

**B) Answer: 25, 24**

The series is

-1, +2, -1, +2 ...

or you may consider it as two AP series

22, 23, 24, ...

and

21, 22, 23, ...

**C) Answer: 15, 19**

This series is also mix of two interleaved sequences:

5, 7, 10, 14, 19 +2 +3 +4 +5

and

6, 8, 11, 15 +2 +3 +4