SSC CGL 2025 Tier-I · 15 September 2025, Shift 1 · Quantitative Aptitude · Question 5 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.

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A container holds a mixture of three liquids A, B, and C in ratio 2 : 3 : 5. If 6 liters of liquid A, 12 liters of liquid B, and a certain amount of liquid C are added to the container, the new ratio of liquids A, B, and C becomes 3 : 5 : 8. Find the quantity (in liters) of liquid C added.

(a)15 liters
(b)16 liters
(c)18 liters
(d)20 liters

Answer

Why

Correct — C. Let the original amounts be 2k, 3k and 5k liters.

Add to A and B: 2k + 6 and 3k + 12
Set them at 3 : 5: 5(2k + 6) = 3(3k + 12)
Expand: 10k + 30 = 9k + 36, so k = 6

Original: A = 12, B = 18, C = 30 liters
New A and B: 18 and 30, which is 3 : 5 at 6 liters a part
New C: 8 parts × 6 = 48 liters

Subtract: 48 − 30 = 18 liters added → option (c)

Why the others are wrong

(a)
15 liters — 15 liters makes C = 30 + 15 = 45, so the mixture is 18 : 30 : 45 = 6 : 10 : 15. The ratio 3 : 5 : 8 needs C at 8 parts of 6, which is 48.
(b)
16 liters — 16 liters makes C = 46, and 18 : 30 : 46 = 9 : 15 : 23, not 3 : 5 : 8. With 6 liters a part, C must reach 48.
(d)
20 liters — 20 liters overshoots: C = 50 against the 48 that 3 : 5 : 8 requires. The mixture would be 18 : 30 : 50 = 9 : 15 : 25.

Concept

Write the old mixture in parts. 2 : 3 : 5 means 2k, 3k and 5k liters for some k. The known additions to A and B turn the new ratio 3 : 5 into an equation in k.

With k = 6 the old mixture is 12, 18 and 30 liters. The new A and B, 18 and 30, fix one part of 3 : 5 : 8 at 6 liters, so the new C is 48 and the amount added is 48 − 30.

Here a part is 6 liters both before and after, so a shortcut also works: A gains 1 part for its 6 liters, B gains 2 parts for its 12, and C's 3 extra parts are 18. Trust the shortcut only after A and B give the same part size, as they do here.

Key facts

Old mixture 12 : 18 : 30 liters, new mixture 18 : 30 : 48 liters.
The new total is 96 liters, and 96 ÷ 16 parts = 6 liters a part.
Two known additions give one equation in k: 5(2k + 6) = 3(3k + 12).

Study next

Mixtures where some quantity is removed before pure liquids are addedAlligation for mixing two solutions of different strengthsThree-term ratios where the value of one part changes

Common traps

Reporting the new amount of C, 48 liters, instead of the amount added, 18.
Assuming the part size stays the same without checking — it holds here, but a different pair of additions would break it.

A three-liquid mixture topped up with pure liquids also decides 14 Sep 2025, 12:30, Quant Q.18, where 30 liters of a 3 : 5 : 2 blend are removed first and the drum started with 150 liters.

15 Sep 2025, 16:00, Quant Q.17 takes 24 liters out of a 5 : 7 : 4 mixture before adding orange and guava juice, and the vessel started with 216 liters.

Related PYQs

No directly related past PYQ was found.

Topic: Mixture and Alligation — all 21 SSC CGL questions on it, every solved shift.