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21, 9, 21, 11, 21, 13, 21, ... What number should come next?
- A14
- B15
- C21
- D23
Correct answer: B
Discussion 1
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CCommunity
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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.
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.