Multiple choice

A series is given with one term missing. Choose the correct option from the given options and complete the series. $5, 6, 9, 15, ?, 40$

  1. $21$
  2. $25$
  3. $27$
  4. $33$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The differences are triangular numbers: 6-5=1, 9-6=3, 15-9=6. Next differences are 10 and 15. So 15+10=25 and 25+15=40.

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