Multiple choice

In the following number series only one number is wrong. Find the wrong number? 7 4 5 9 20 51

  1. 20

  2. 9

  3. 5

  4. 51

  5. 7
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The pattern is: multiply by 2 and add 2, 3, 4, 5, 6 respectively. Checking: 7 × 2 + 2 = 16, 16 × 2 + 3 = 35, 35 × 2 + 4 = 74, 74 × 2 + 5 = 153, 153 × 2 + 6 = 312. This gives us: 7, 16, 35, 74, 153, 312. The given sequence has 4, 5, 9, 20, 51 instead. Testing different patterns reveals 51 breaks the pattern when other numbers follow a different rule.

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