SSC CGL 2025 Tier-I · 17 September 2025, Shift 2 · General Intelligence and Reasoning · Question 20 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.

In a 40 L solution, the ratio of acid to water is 5:3. How much water must be added to make it 1:1?

(a)5 L
(b)6 L
(c)17 L
(d)10 L

Answer

Why

Correct — D.
Rule: only water is added, so the acid stays fixed.

Acid = 5⁄8 × 40 = 25 L
Water = 3⁄8 × 40 = 15 L

For 1:1, water must equal acid = 25 L
Water to add = 25 − 15 = 10 L → option (d).

Why the others are wrong

(a)
5 L — 5 L takes the water to 20 L against 25 L of acid, a ratio of 5:4. The mixture is still acid-heavy.
(b)
6 L — 6 L takes the water to 21 L against 25 L of acid, 25:21. Water must reach 25 L to match the acid.
(c)
17 L — 17 L overshoots: water becomes 32 L against 25 L of acid, so the mixture ends up with more water than acid.

Concept

In a dilution problem the component you do not add stays fixed. Split the 40 L by the ratio 5:3, which is 8 parts of 5 L each, to get 25 L of acid and 15 L of water.

A 1:1 ratio needs water equal to acid, so the water must rise from 15 L to 25 L. The difference is what you add.

The parts route is quicker. Acid is 5 parts and stays 5. For 1:1 the water must also be 5 parts. It is 3 now, so add 2 parts, and one part is 40 ÷ 8 = 5 L, giving 10 L.

Key facts

40 L in the ratio 5:3 is 25 L acid and 15 L water (one part = 5 L).
Adding water changes only the water, so the acid stays 25 L.
At 1:1 the mixture holds 25 L of each, 50 L in all.

Study next

Adding water to reach a target percentage rather than a ratioRemoving some mixture and replacing it with one pure componentAlligation for mixing two solutions of different strengths

Common traps

Making the water half of the original 40 L (20 L) and adding 5 L, forgetting that the total grows
Adding 25 L, the acid amount, instead of the difference 25 − 15

23 Sep 2024, 09:00, Quant Q.20 is the same set-up with milk: 32 L at 5:3, water added until it is 50%, keyed 8 litres.

14 Sep 2025, 16:00, Quant Q.11 runs it backwards: acid and water at 5:3 become 5:4 after 4 L of water, keyed original acid 20 litres.

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