Question

In each of the questions below, one term in the given number series is wrong. Find out the wrong term.
11, 5, 20, 12, 40, 26, 74, 54

• A. 5
• B. 20
• C. 40
• D. 26

Hint:

Split the series into alternate (odd-position and even-position) sub-series and check each one for a pattern.

Answer 1

The Correct Option is C

An alternate way is to test each candidate value directly by checking whether removing it restores a clean pattern in its own alternate sub-series.

1. 5: This is an even-position term. The even sub-series 5, 12, 26, 54 already increases by 7, 14, 28, a perfectly doubling pattern, so 5 is not the error.
2. 20: This is an odd-position term. Removing 20 breaks the chain between 11 and 40, since we would then need to explain 11 to 40 directly, which does not fit a clean doubling-difference pattern starting from 9. So 20 is not the error.
3. 40: This is an odd-position term. The odd sub-series is 11, 20, 40, 74. Testing the doubling-difference pattern 9, 18, 36 on 11 gives 11, 20, 38, 74, which fits perfectly if 40 is replaced by 38. So 40 is the error.
4. 26: This is an even-position term, and as shown above, the even sub-series 5, 12, 26, 54 is already fully consistent, so 26 is not the error.

Only replacing 40 with 38 makes both sub-series consistent, confirming the wrong term is 40. $\boxed{40}$