Which number is next 2 7 8 3 12 9

The correct answer is: 4

Explanation:

In the given series, there are three sub-series, which are as follows:

Series-1: 2, 3,?

Series-2: 7, 12,?

Series-3: 8, 9,?

In series-1, "1" is being added to every number. Hence, the next number is 4.

In series-2, "5" is being added to every number, Hence, the number next to 4 will be 17.

In series-3, "1" is being added to every number. Hence, the next number to 17 will be 10.

But as the question is asked about the next number to 9, hence the correct answer will be 4.