Multiple choice

Find the missing number in the given below series. $7 \,\,\,\, 28 \,\,\,\, 63 \,\,\,\, ? \,\,\,\, 215 \,\,\,\, 344$

  1. 86

  2. 120

  3. 126

  4. 99

  5. 112
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The series follows a pattern of cubes plus/minus 1: 2³-1=7, 3³+1=28, 4³-1=63, 5³+1=126, 6³-1=215, 7³+1=344. Each term alternates between (n³-1) and (n³+1) where n starts at 2 and increases by 1 each time. The missing term is 5³+1=125+1=126.

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