2, 2 1/2, 1 1\2, 2 whats the next number in the series

Explanation:

The jump from 2 to 2&1/2 is an increase of 1/2

2 + 1/2 = 2 & 1/2

The jump from 2 & 1/2 to 1 & 1/2 is a decrease of 1

(2 & 1/2) - 1 = (2 - 1) & 1/2 = 1 & 1/2

The jump from 1 & 1/2 to 2 is an increase of 1/2

(1 & 1/2) + 1/2 = 1 + (1/2 + 1/2) = 1 + 1 = 2

The pattern seems to be "add 1/2, subtract 1". Assuming this is the case, we would then subtract 1 from the last term we got (2) to get 2-1 = 1