Multiple choice general knowledge math & puzzles

Look at this series: 21, 9, 21, 11, 21, 13, 21, ... What number should come next?

  1. 14

  2. 15

  3. 21

  4. 23
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

This series alternates between 21 and an increasing odd number. Odd positions: 21, 21, 21, 21 (constant). Even positions: 9, 11, 13, __ (increasing by 2 each time). So the next number is 13 + 2 = 15. Option A (14) would be if it increased by 1. Option C (21) is the constant value at odd positions.

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