Multiple choice

Find out the wrong number from the given series. 20, 21, 43, 140, 521, 2606

  1. 20

  2. 21

  3. 43

  4. 140

  5. 521
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The pattern is: 20*1+1=21, 21*2+1=43, 43*3+1=130 (not 140), 130*4+1=521, 521*5+1=2606. The number 140 is incorrect.

AI explanation

The pattern multiplies each number by an increasing integer and then alternates adding and subtracting 1: 20 × 1 + 1 = 21, 21 × 2 + 1 = 43, 43 × 3 + 1 = 130 (not 140), 130 × 4 + 1 = 521, and 521 × 5 + 1 = 2606. The correct number should be 130 instead of 140.

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