Question

Find out the missing number in the following series: 6, 11, 21, ?, 56, 81

• A. 42
• B. 36
• C. 91
• D. 51

Hint:

When dealing with number series, always check if the difference between terms forms a simple sequence — arithmetic progression in differences is common.

Answer 1

The Correct Option is B

Let’s examine the pattern step-by-step.
We are given the series: $6, 11, 21, ?, 56, 81$
Step 1: Check the differences between consecutive terms.
$11 - 6 = 5$
$21 - 11 = 10$
The differences are increasing. Let’s continue:
We expect the next difference to be $+15$:
$21 + 15 = 36$
Step 2: Check consistency with the following terms.
$56 - 36 = 20$ (next difference increased by 5 again).
$81 - 56 = 25$ (again increased by 5).
So the difference sequence is: $+5, +10, +15, +20, +25$.
Thus, the missing term is $\mathbf36$.