SSC CGL 2025 Tier-I · 21 September 2025, Shift 1 · General Intelligence and Reasoning · Question 13 of 99

We transcribed this text from the pictures on a candidate's response sheet for this shift; the answer is the key SSC colour-marked on that sheet. Solution last reviewed 13 September 2026.

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SSC does not publish CGL question papers or a public answer key. From 2025 the candidate response sheet prints every question and option as a picture, so the text here is transcribed from those pictures for this shift and checked against them independently; where the layout carries meaning, the picture is shown as well. Each answer is the key SSC colour-marked on that sheet. SSC released a tentative key for challenge and later its final one, both only to candidates behind a login, and the sheet does not say which of the two it carries. The solutions are written by UnlockIAS.

Find the next number in the series: 3, 9, 27, 81, ?, 729

(a)243
(b)218
(c)270
(d)261

Answer

Why

Correct — A.
Rule: each term is 3 times the one before (powers of 3).

3 × 3 = 9, 9 × 3 = 27, 27 × 3 = 81
Next: 81 × 3 = 243
Check: 243 × 3 = 729, the term after the gap

? = 243 → option (a).

Why the others are wrong

(b)
218 — 218 × 3 = 654, not 729. It also breaks the ×3 step from 81, since 81 × 3 = 243.
(c)
270 — 270 × 3 = 810, which overshoots 729. It is not a power of 3 either: 270 = 2 × 3³ × 5.
(d)
261 — 261 × 3 = 783, not 729, and 261 ÷ 81 is not a whole number. It fits no step of the series.

Concept

A number series with a fixed ratio grows by multiplication, not addition. Divide each term by the one before: 9 ÷ 3, 27 ÷ 9 and 81 ÷ 27 all give 3.

So the terms are powers of 3: 3¹, 3², 3³, 3⁴, and the gap is 3⁵ = 243. The last term, 729 = 3⁶, confirms it.

The term after the gap is a free check. A value that does not give 729 when multiplied by 3 cannot fill the blank, and that rules out 218, 270 and 261 at once.

Key facts

3⁵ = 243 and 3⁶ = 729.
In a geometric series each term divided by the one before gives the same ratio.
The powers of 3 run 3, 9, 27, 81, 243, 729.

Study next

Wrong-number series where one term breaks a ×3 patternSeries with alternating operations such as ×2 then +3Number sets related as n, n² and n³

Common traps

Looking for a constant difference, though the gaps 6, 18 and 54 are not equal
Ignoring the term after the gap, which checks the answer: 243 × 3 = 729

23 Sep 2024, 12:30, Reasoning Q.18 builds on the same powers: (3, 9, 27) and (4, 16, 64) are n, n² and n³, keyed (7, 49, 343) (option c).

24 Sep 2025, 16:00, Reasoning Q.16 hides a wrong term in a ×3 series: 2, 6, 18, 54, 162, 325, keyed 325 (option d), since 162 × 3 = 486.

Related PYQs

No directly related past PYQ was found.

Topic: Number Series — all 178 SSC CGL questions on it, every solved shift.