SSC CGL 2025 Tier-I · 24 September 2025, Shift 2 · General Intelligence and Reasoning · Question 17 of 100

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.

Where this paper and its answers come from

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.

What should come at the place of question mark? : 625, 125, 25, 5, ?, ?

(a)1, 1
(b)2, 1
(c)1, 0.2
(d)0.5, 0.1

Answer

Why

Correct — C.
Rule: divide by 5 at every step.

625 ÷ 5 = 125
125 ÷ 5 = 25
25 ÷ 5 = 5

First blank: 5 ÷ 5 = 1
Second blank: 1 ÷ 5 = 0.2 → option (c).

Why the others are wrong

(a)
1, 1 — 1, 1 gets the first blank right but then stops dividing. The rule does not end at 1: 1 ÷ 5 is 0.2.
(b)
2, 1 — 2, 1 breaks the rule at once, since 5 ÷ 5 is 1, not 2. The step 2 → 1 then halves, which the series never does.
(d)
0.5, 0.1 — 0.5, 0.1 opens with 5 ÷ 10. The divisor is fixed at 5, so the first blank is 5 ÷ 5 = 1, and 0.5 never appears.

Concept

This is a geometric series: each term is the one before multiplied by the same ratio, here 1⁄5.

Written as powers, the terms are 5⁴, 5³, 5², 5¹, so the blanks are 5⁰ = 1 and 5⁻¹ = 0.2.

If you expect whole numbers, 1 looks like the end of the line. It is not: dividing by 5 carries on into decimals.

Key facts

625 = 5⁴, 125 = 5³, 25 = 5², 5 = 5¹.
5⁰ = 1 and 5⁻¹ = 1⁄5 = 0.2.
A constant ratio between terms makes a geometric series.

Study next

Geometric series with a ratio of 1⁄2 or 1⁄3 running into fractionsWrong-term questions on a × 4 seriesSeries that multiply by a growing factor (× 1, × 2, × 3)

Common traps

Treating 1 as the end of the series and repeating it
Switching to ÷ 10 once the terms get small, which gives 0.5, 0.1

26 Sep 2025, 12:30, Reasoning Q.15 prints the start of this same series, 625, 125, 25, ___, keyed 5. This question pushes two steps further, past 1 into a decimal.

Related PYQs

No directly related past PYQ was found.

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