Answer:
We have to determine the pattern of numbers followed in the sequence 2, 7, 8, 3, 12, 9.
Do a grouping of the sequence into two groups. Let the first group be 2, 7, 8 and the second group be 3, 12, 9
There is a difference of 1 in the pair 2 and 3, a difference of 5 in the pair 7 and 12 and a difference of 1 in the pair 8 and 9
This means there would be a difference of 5 in the next pair.
So, adding 5 to the first number to the third pair.
Hence, the next number will be 13.