Odd Man Out and Series - General Aptitude

Q1:

3, 7, 6, 5, 9, 3, 12, 1, 15, (....)

A 18

B 13

C -1

D 3

ANS:C - -1

There are two series, beginning respectively with 3 and 7. In one 3 is added and in another 2 is subtracted. The next number is 1 - 2 = -1.