Look at this series: 7, 10, 8, 11, 9, 12, ... What number should come next?

This is an alternating series. The first pattern adds 3 (7, 10; 8, 11; 9, 12) and the second pattern subtracts 2 (10, 8; 11, 9). After 12, the next step follows the 'subtract 2' rule from the previous peak, but more simply, the sequence is (7, 8, 9...) and (10, 11, 12...). The next number in the second sub-sequence is 10? No, the next number is 10 because it follows 9 (9+1). Wait, the sequence is 7(+3), 10(-2), 8(+3), 11(-2), 9(+3), 12(-2) = 10.