Look at this series: 21, 9, 21, 11, 21, 13, 21, ... What number should come next?
Pick one:
A) 14	B) 15	C) 21	D) 23	E) None of these
Explanation:   In this alternating repetition series, the random number 21 is interpolated every other number into an otherwise simple addition series that increases by 2, beginning with the number 9.   Answer is 15
<result>B</result>
Look at this series: 21, 9, 21, 11, 21, 13, 21, ... What number should come next?