Multiple choice

Directions: Complete the series.

1, 2, 5, 11, 21, ?

  1. 36

  2. 31

  3. 27

  4. 24

  5. 22
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A Correct answer
Explanation

From the series, it is clear that successive terms of the series are added to 1, 1 + 2, 1 + 2 + 3..... to get the next terms in the following way:

1 + 1 = 2

2 + (1 + 2) = 5  

5 + (1 + 2 + 3) = 11  

11 + (1 + 2 + 3 + 4) = 21  

Similarly, 21 + (1 + 2 + 3 + 4 + 5) = 36

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