Question

Identify the sixth number in the series: 6, 11, 21, 36, 56, ?

• A. 52
• B. 21
• C. 81
• D. 82

Hint:

If the first level of differences between terms in a series is not constant, find the second level of differences (the difference of the differences). If that is constant, you have found the pattern. This is a common type of series problem.

Answer 1

The Correct Option is C

This is a series with a pattern in its differences. Let's find the first level of differences between consecutive terms. 11 - 6 = 5 21 - 11 = 10 36 - 21 = 15 56 - 36 = 20 The differences are 5, 10, 15, 20. This is a simple arithmetic progression with a common difference of 5. The next difference in this sequence should be 20 + 5 = 25. To find the next term in the original series, we add this next difference to the last term. Next term = 56 + 25 = 81. The sixth number in the series is 81.