Home » Aptitude » Odd Man Out and Series

Number series — choose the odd number (all others are divisible by 11): 22, 33, 66, 99, 121, 279, 594

Difficulty: Easy

Correct Answer: 279

Explanation:

Introduction / Context:
This odd-one-out question checks divisibility recognition. A quick way to spot the outlier is to see if all but one term share a common factor or property (e.g., multiples of a fixed base).

Given Data / Assumptions:

Series: 22, 33, 66, 99, 121, 279, 594
Pick the single number that does not match the common property.

Concept / Approach:
Test each value for divisibility by 11. Many in the list obviously relate to 11: 22 (211), 33 (311), 66 (611), 99 (911), 121 (11^2), 594 (5411). The standard 11-divisibility check uses alternating-digit sums.

Step-by-Step Solution:

22, 33, 66, 99, 121, and 594 are all multiples of 11.Check 279: Sum of digits in odd places minus sum in even places = (2 + 9) − (7) = 11 − 7 = 4, not 0 or a multiple of 11.Therefore, 279 is not divisible by 11.

Verification / Alternative check:

Compute 279 / 11 = 25.36… (not an integer), confirming it is the outlier.

Why Other Options Are Wrong:

33, 121, 594: Each is a clear multiple (311, 1111, 5411), so they match the common property.

Common Pitfalls:

Overlooking 121 as 11^2, or assuming every number that “looks large” might be special without checking divisibility.

Number series — choose the odd number (all others are divisible by 11): 22, 33, 66, 99, 121, 279, 594

More Questions from Odd Man Out and Series

Discussion & Comments