Look at this series: 21, 9, 21, 11, 21, 13, 21, ... What number should come next?
Select.
A) 14
B) 15
C) 21
D) 23
E) 24
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: Option 15
<result>B</result>
Look at this series: 21, 9, 21, 11, 21, 13, 21, ... What number should come next?