Q.Find the missing number in the series: 3, 6, 11, 18, 27, ?

Write out the differences between consecutive terms first — the pattern is in the differences, not the terms themselves.

Differences: 6-3=3, 11-6=5, 18-11=7, 27-18=9. Each difference is 2 more than the previous one, so the next difference is 9+2=11.

27+11=38.

Writing out the difference between each pair of consecutive terms:

6-3=3

11-6=5

18-11=7

27-18=9

The differences themselves form a series: 3, 5, 7, 9 — each one exactly 2 more than the one before it. Following this pattern, the next difference must be 9+2=11.

Adding this difference to the last given term: 27+11=38.

A common error is assuming a constant difference (like a simple arithmetic series) throughout, without first checking whether the differences themselves are changing in a pattern — here the difference genuinely increases by 2 each time, rather than staying fixed.