SSC CGL 2024 Tier-I · 24 September 2024, Shift 2 · General Intelligence and Reasoning · Question 23 of 100

Text as printed on a candidate's response sheet for this shift; answer per SSC's tentative key as marked on that sheet. Solution last reviewed 10 September 2026.

Where this paper and its answers come from

SSC does not publish CGL question papers or a public answer key. The questions and options here are reproduced as printed on a candidate's own response sheet for this shift — the Commission's text, unchanged. Each answer is SSC's tentative key as marked on that sheet; SSC allowed challenges to it and never publishes a final key. The solutions are written by UnlockIAS.

The second number in the given number-pairs is obtained by performing certain mathematical operation(s) on the first number. The same operation(s) is/are followed in all the number-pairs, except one. Find that odd number-pair. (NOTE: The relation should be found without breaking down the numbers into its constituent digits)

(a)18 : 306
(b)13: 182
(c)25 : 650
(d)23 : 552

Answer

Why

Correct — A. Divide the second number by the first before doing anything else.

306 ÷ 18 = 17
182 ÷ 13 = 14
650 ÷ 25 = 26
552 ÷ 23 = 24

Rule: three of the four run second = n × (n + 1). 13 × 14 = 182, 25 × 26 = 650 and 23 × 24 = 552 all fit.

18 does not. 18 × 19 = 342, but the paper prints 306, and 306 is 18 × 17 — the multiplier runs the wrong way.

So 18 : 306 is the odd pair, option (a).

Why the others are wrong

(b)
13: 182 — 13 × 14 = 182, so this pair follows the n × (n + 1) rule and belongs with the majority rather than outside it.
(c)
25 : 650 — 25 × 26 = 650, another clean n × (n + 1) fit. The large second number makes it look unusual, but the arithmetic is orthodox.
(d)
23 : 552 — 23 × 24 = 552. These are the biggest numbers on offer, which is the whole trap — size is not oddness, and this pair fits.

Concept

Odd-one-out number pairs are decided by finding the rule that three of the four share, not by finding something peculiar about one of them.

Take the quotient first, because it is one line of work and it exposes the family instantly. Three quotients here come out one more than the first number, and one comes out one less.

The note printed with the question bars splitting a number into digits, so digit sums and digit reversals are not available as explanations.

Both n × (n + 1) and n × (n − 1) are a number multiplied by its neighbour, so all four pairs look alike at a glance. Which neighbour is the entire question.

Key facts

18 × 17 = 306, while 18 × 19 = 342.
13 × 14 = 182, 25 × 26 = 650 and 23 × 24 = 552 all follow n × (n + 1).
Dividing the second number by the first exposes the rule in a single step.

Study next

n × (n + 1) and n² + n as the same relation written two waysOdd-one-out number pairs solved by taking quotients firstNumber pairs built on n², n³ and n² ± n

Common traps

Testing the pairs in the printed order and stopping at the first one that works
Reading 306 as 18 × 19 out of habit and passing over the odd pair
Splitting the numbers into digits, which the printed note forbids

The same odd-pair wrapper, with the same whole-number note, is set at 19 Sep 2024, 12:30, Reasoning Q.16, where the keyed odd pair is 784 : 961.

Related PYQs

No directly related past PYQ was found.