In the following question, one term in the number series is wrong. Find the…
2024
In the following question, one term in the number series is wrong. Find the wrong term.
3, 2, 8, 12, 13, 24, 18, 32, 23, 42
- A.
12
- B.
13
- C.
18
- D.
24
Show answer & explanation
Correct answer: D
CONCEPT: When a number series does not show one steady pattern from term to term, check whether it is actually two series interleaved together -- one running on the odd positions and another on the even positions. Split the terms accordingly and verify each half independently has its own constant common difference; whichever half breaks its own constant difference contains the wrong term.
Write the series with its position number: 3 (1st), 2 (2nd), 8 (3rd), 12 (4th), 13 (5th), 24 (6th), 18 (7th), 32 (8th), 23 (9th), 42 (10th).
Take all the odd-position terms together: 3, 8, 13, 18, 23.
Take all the even-position terms together: 2, 12, 24, 32, 42.
Check the odd-position set: 8-3=5, 13-8=5, 18-13=5, 23-18=5 -- a constant step of +5 throughout, so there is no break here.
Check the even-position set: 12-2=10, 24-12=12, 32-24=8, 42-32=10 -- the step size is not constant; it changes right at the 6th term of the original series.
The even-position set should also move with a constant step of +10 (matching 2 to 12), so the 6th term of the original series is the one that has gone wrong.
CROSS-CHECK: Restoring a constant +10 step through the even-position set (2, 12, 22, 32, 42) makes every consecutive gap equal to 10, confirming that the 6th term of the original series is the wrong one; the odd-position set was never touched and stays consistent throughout.
ANSWER: 24 is the wrong term in the series.