Number series – find the wrong term (identify the outlier) Series: 125, 126, 124, 127, 123, 129

Introduction / Context:
This is a classic alternating-increment/decrement pattern. The rule adds and subtracts consecutive integers in turn; one number breaks the rhythm.

Given Data / Assumptions:

• Series: 125, 126, 124, 127, 123, 129.
• Exactly one wrong term.

Concept / Approach:
Check if the series alternates between “+k” and “−(k+1)” for k = 1, 2, 3, … A standard form is: +1, −2, +3, −4, +5, −6, …

Step-by-Step Solution:

Verification / Alternative check:
Continuing the pattern after the correction would require the next step to be −6. Since only one term must be wrong, 129 is the outlier (should have been 128).

Why Other Options Are Wrong:

• 126, 124, 123 all fit the alternating +1, −2, +3, −4 pattern exactly; removing any of them ruins the clean alternation.

Common Pitfalls:
Trying a fixed-difference rule; ignoring that alternating increase/decrease with step sizes 1, 2, 3, 4, … is a well-used pattern in reasoning tests.

Final Answer:
129