SSC CGL 2024 Tier-I · 13 September 2024, Shift 1 · General Intelligence and Reasoning · Question 16 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.

Three of the following numbers are alike in a certain way and one is different. Pick the odd one out. (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 /deleting /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)31 – 5 – 160
(b)13 – 8 – 109
(c)21 – 4 – 89
(d)27 – 9 – 243

Answer

Why

Correct — D. Run the same arithmetic on all four triples; the one that breaks is the answer.

Rule: first × second + 5 = third.

31 × 5 = 155, and 155 + 5 = 160
13 × 8 = 104, and 104 + 5 = 109
21 × 4 = 84, and 84 + 5 = 89

27 × 9 = 243, and 243 + 5 = 248, not the 243 printed. Option (d) is the triple whose third number is the bare product with no + 5, so it is the odd one out.

Why the others are wrong

(a)
31 – 5 – 160 — Option (a) obeys the rule: 31 × 5 = 155 and 155 + 5 = 160, the number printed. It sits with the group, so it cannot be the exception.
(b)
13 – 8 – 109 — Option (b) obeys the rule: 13 × 8 = 104 and 104 + 5 = 109. Nothing separates it from the other two conforming triples.
(c)
21 – 4 – 89 — Option (c) obeys the rule: 21 × 4 = 84 and 84 + 5 = 89. Its numbers are the smallest of the four, but size is not the relation being tested.

Concept

Odd-one-out on number triples asks for the one arithmetic rule that three of the four obey. SSC's note does real work: you may operate on 27 and 9 as whole numbers, but you may not split 27 into 2 and 7.

Start with multiplication, because the third number is far larger than the first two. Compute first × second for every row, then look at the gap to the third number.

When three gaps agree and one differs you have the rule and the answer in a single pass. Here the gaps are 5, 5, 5 and 0.

The rule is a product plus a constant, so the odd row is not the one that fails to multiply — it is the one that needs no constant at all.

Key facts

The shared rule is first × second + 5 = third.
27 × 9 = 243 exactly, so option (d) has a gap of 0 where the others have 5.
SSC's note forbids digit-splitting, so 27 may not be worked as 2 and 7.

Study next

Odd-one-out triples where the rule is first × second minus a constantNumber-triple analogies, where a fifth set must match the given pattern

Common traps

Stopping at the first row that multiplies cleanly and calling it the exception.
Seeing that 9, 27 and 243 are all powers of 3 and building a rule only one row supports.
Splitting the two-digit numbers into digits, which the question's note rules out.

The same template with a different constant is at 18 Sep 2024, 9:00, Reasoning Q.22, where the rule is first × second minus 5 and the odd row, 25 – 7 – 175, is again the bare product.

At 12 Sep 2024, 12:30, Reasoning Q.12 the relation changes shape entirely to (first + second) × 11, so do not carry the multiply-then-add habit over blindly.

Related PYQs

No directly related past PYQ was found.