Question - Look at this series: 21, 9, 21, 11, 21, 13, 21, ... What number should come next?
A. 14
B. 15
C. 21
D. 23
Answer -
B) 15
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.