Multiple choice

Find the missng term in the following number series- 15 19 47 117 247 ?

  1. 390

  2. 296

  3. 340

  4. 455

  5. None of these
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Find the pattern in the differences: 19-15=4, 47-19=28, 117-47=70, 247-117=130. Now find second-level differences: 28-4=24, 70-28=42, 130-70=60. Third-level differences: 42-24=18, 60-42=18. The third-level differences are constant at 18. So next second-level difference is 60+18=78, next first-level difference is 130+78=208, and next term is 247+208=455. Alternatively, the pattern is n^3 - n^2 for n=2,3,4,5,6: 2^3-2^2=8-4=4, 3^3-3^2=27-9=18... no that doesn't match. Let me verify: 15+4=19, 19+28=47, 47+70=117, 117+130=247, 247+208=455. Yes, 455 is correct.

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