Multiple choice

Find the wrong number in the following series. $6, 9, 15, 22, 51, 99$

  1. $99$
  2. $51$
  3. $22$
  4. $15$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Check each term with the pattern: n-2 × 2 + (n-2)/2 = current term. 6: base case. 9: 6×2 + 3 = 15 ✓. 15: 9×2 + 4.5 = 22.5 ✗ (should be 22.5). 22 should be 22.5. 51: 15×2 + 7.5 = 37.5 ✗ (should be 37.5). 99: If 22 were 22.5, then 22.5×2 + 11 = 56 ✗. The pattern breaks at 22, making it the wrong number.

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