Multiple choice

Find the missing term in the following number series. ? 5 23 59 119 209

  1. 2

  2. 1

  3. -1

  4. -3

  5. 4
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Working backwards, the series has a constant third difference of 6. With ?=-1, the differences are: -1→5 (+6), 5→23 (+18), 23→59 (+36), 59→119 (+60), 119→209 (+90). Second differences: 12, 18, 24, 30. Third differences: 6, 6, 6 (constant).

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