SSC CGL 2024 Tier-I · 11 September 2024, Shift 1 · General Intelligence and Reasoning · Question 21 of 95

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.

8 is related to 512 following a certain logic. Following the same logic, 12 is related to 1728. To which of the following is 15 related, following the same logic? (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)3375
(b)2725
(c)3735
(d)2275

Answer

Why

Correct — A. Rule: second number = first number cubed.

8³ = 8 × 8 × 8 = 512, which matches the first pair.
12³ = 12 × 12 × 12 = 1728, which matches the second pair.

Apply it to 15:
15² = 225
225 × 15 = 3375 → option (a).

Why the others are wrong

(b)
2725 — 2725 lies below 14³ = 2744, so it cannot be the cube of 15. Cubes climb fast: after 12³ = 1728 come 2197, 2744 and then 3375.
(c)
3735 — 3735 is 3375 with two digits swapped. It fails a divisibility check: 15³ = 27 × 125, so the answer must divide exactly by 125, and 3735 does not.
(d)
2275 — 2275 sits between 13³ = 2197 and 14³ = 2744, so it is not a cube of any whole number, let alone of 15.

Concept

Number-pair analogies are cracked by testing a short ladder of whole-number relations: difference, ratio, square, cube, then compounds such as n² + n. A cube announces itself by the size of the jump — 8 to 512 is a factor of 64, far too large for a ratio or a square.

The NOTE matters as much as the arithmetic. It bars reading 512 as 5, 1, 2, so the only legitimate move is an operation on 8 as a whole number, and cubing is the one that also fits 12 → 1728.

Knowing the cubes up to 20 by heart turns this into a recall item. 13³ = 2197, 14³ = 2744 and 15³ = 3375, and those three values alone eliminate every wrong option here.

Key facts

8³ = 512 and 12³ = 1728, which fixes the relation as cubing.
15³ = 3375.
The neighbouring cubes are 13³ = 2197 and 14³ = 2744.
15³ factorises as 27 × 125, so the answer must be divisible by 125.

Study next

Cubes and cube roots up to 20, recalled rather than computedNumber-pair sets asking for the odd pair out under a square or cube ruleSeparating n³ from n³ + n and n³ − n in pair analogies

Common traps

Reading 8 → 512 as a ×64 ratio, which then fails at 12 → 1728.
Picking a digit-shuffled near-miss such as 3735 without a divisibility check.
Breaking 512 into digits, which the bracketed NOTE forbids.

The same frame appears with the operation reversed at 24 Sep 2024, 16:00, Reasoning Q.3 (64 → 4 and 216 → 6, a cube root), and with squares at 25 Sep 2024, 09:00, Reasoning Q.23 (11 → 121 and 22 → 484). Reasoning Q.20 of the same paper runs the frame as a plain ×7.

Related PYQs

No directly related past PYQ was found.