SSC CGL 2025 Tier-I · 19 September 2025, Shift 1 · General Intelligence and Reasoning · Question 21 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 11 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.

If 4 taps can fill a tank in 15 minutes, how many taps are needed to fill it in 6 minutes?

(a)10
(b)8
(c)6
(d)5

Answer

Why

Correct — A.
Rule: taps × minutes stays constant for the same tank.

Work in the tank = 4 taps × 15 min = 60 tap-minutes
Taps for 6 min = 60 ÷ 6 = 10 taps → option (a).

Why the others are wrong

(b)
8 — 8 taps × 6 min = 48 tap-minutes, short of the 60 the tank needs. 8 taps would take 60 ÷ 8 = 7.5 minutes.
(c)
6 — 6 taps × 6 min = 36 tap-minutes, only 60% of the tank. 6 taps would need 10 minutes.
(d)
5 — 5 taps × 6 min = 30 tap-minutes, half the tank. 5 taps would need 12 minutes.

Concept

With identical taps, filling the tank takes a fixed amount of work, so taps × time stays the same. More taps means less time: an inverse proportion.

Count the work in tap-minutes (4 × 15 = 60), then divide by the time you want: 60 ÷ 6 = 10 taps.

The question assumes every tap flows at the same rate. If the taps had different rates, you would add their rates instead of counting taps.

Key facts

Inverse proportion: taps₁ × time₁ = taps₂ × time₂.
Here 4 × 15 = 10 × 6 = 60 tap-minutes.
Cutting the time to 6⁄15 of the original multiplies the taps by 15⁄6: 4 × 15⁄6 = 10.

Study next

Men-and-days work problems (M₁ × D₁ = M₂ × D₂)Two pipes with different rates filling one tankInlet and outlet pipes working at the same time

Common traps

Treating it as direct proportion: 4 × 6⁄15 = 1.6 taps, when less time needs more taps, not fewer
Dividing 15 by 6 and stopping at 2.5, without multiplying by the 4 taps

26 Sep 2024, 09:00, Quant Q.21 measures a tank the same way: with the slow pipe as 1 unit and the fast one as 4, the two together fill 5 × 48 = 240 units, so the slow pipe alone is keyed 240 minutes.

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