SSC CGL 2024 Tier-I · 10 September 2024, Shift 2 · General Intelligence and Reasoning · Question 7 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 6 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.

Three of the following number-pairs are alike in some manner and hence form a group. Which number-pair does not belong to that group? (NOTE: Operations should be performed on the whole numbers, without breaking down the numbers into its constituent digits. E.g. 13 – Operations on 13 such as adding/subtracting/multiplying etc. to 13 can be performed. Breaking down 13 into 1 and 3 and then performing mathematical operations on 1 and 3 is not allowed.)

(a)15 – 240
(b)18 – 306
(c)22 – 462
(d)21 – 420

Answer

Why

Correct — A. Test each pair as a number multiplied by the number next to it.

18 × 17 = 306
22 × 21 = 462
21 × 20 = 420

Rule: second number = first × (first − 1).

Now the odd pair. 15 × 14 = 210, not 240. The printed 240 is 15 × 16, the neighbour on the other side.

Three pairs multiply downwards and one multiplies upwards, so 15 – 240 is the exception, option (a).

Why the others are wrong

(b)
18 – 306 — 18 × 17 = 306, the same downward multiplication used by 22 – 462 and 21 – 420. It belongs to the group.
(c)
22 – 462 — 22 × 21 = 462, again first × (first − 1). Nothing separates it from the other two members.
(d)
21 – 420 — 21 × 20 = 420, which fits the rule exactly. Only the 15 pair multiplies by the number above rather than below.

Concept

Odd-one-out items on number pairs are solved by finding the rule that three of them share, not by hunting for something odd about one.

When the second number is far larger than the first, try products of consecutive integers. n × (n − 1) is the same as n² − n, so squares you already know give the answer instantly: 22² = 484, minus 22, is 462.

The trap here is that all four pairs are products of consecutive numbers. What separates them is direction — three go down, one goes up.

Because 240 = 15 × 16 is also a product of consecutive integers, a candidate who stops at 'consecutive product' finds all four options valid and no odd one out. The rule has to be stated with its direction.

Key facts

n × (n − 1) equals n² − n, so 18² − 18 = 306 and 22² − 22 = 462.
15 × 14 = 210, while the pair prints 240, which is 15 × 16.
The whole-number note bars splitting 240 into 2, 4 and 0.

Study next

Products of consecutive integers, n(n − 1) and n(n + 1)Odd-one-out sets where three members share a rule and the fourth reverses itSquares up to 30, which make n² − n instant

Common traps

Stopping at 'all four are consecutive products' without checking the direction.
Testing only two pairs, when 18, 21 and 22 agree and 15 is the single exception.
Working on digit sums, which the stem forbids.

This shift's Reasoning section carries the same whole-number note at Q.2, Q.5 and Q.12 (10 Sep 2024, 12:30). Each time the intended operation is on the number itself, never on its digits.

Related PYQs

No directly related past PYQ was found.