Multiple choice

Choose the correct alternatives from given ones that will 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

Completing the series: 5, 6, 9, 15, ?, 40. Pattern: Differences are 6-5=1, 9-6=3, 15-9=6. The differences themselves follow pattern: 1, 3, 6 (which are triangular numbers: 1, 1+2, 1+2+3). Next difference should be 10 (1+2+3+4), so next term = 15+10=25. Verifying: Next difference would be 15, so 25+15=40, which matches. Alternatively, each term is previous term plus position: 5+1=6, 6+3=9, 9+6=15, 15+10=25, 25+15=40. Therefore, answer is 25 (option B).

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