SSC CGL 2025 Tier-I · 22 September 2025, Shift 1 · Quantitative Aptitude · Question 16 of 98

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 45-litre mixture of kerosene and diesel contains kerosene and diesel in the ratio 4:5. How much diesel must be added to make the ratio 4:6?

(a)3 L
(b)5 L
(c)6 L
(d)7.5 L

Answer

Why

Correct — B. Only diesel is added, so the kerosene stays fixed. Split the 45 L first.

One ratio part: 45 ÷ (4 + 5) = 5 L
Kerosene = 4 × 5 = 20 L, diesel = 5 × 5 = 25 L
Diesel needed for 4 : 6 = 20 × 6⁄4 = 30 L

Diesel to add = 30 − 25 = 5 L → option (b)

Why the others are wrong

(a)
3 L — 3 L brings diesel to 28 L, and 20 : 28 = 5 : 7, not 4 : 6. Diesel has to reach 30 L.
(c)
6 L — 6 L brings diesel to 31 L, so kerosene to diesel becomes 20 : 31, just past the 20 : 30 that 4 : 6 requires.
(d)
7.5 L — 7.5 L brings diesel to 32.5 L: 20 : 32.5 = 8 : 13, which overshoots the target 20 : 30.

Concept

When only one liquid is added to a mixture, the other liquid does not change, so it anchors the new ratio.

Find the fixed quantity first (20 L of kerosene), then read off what the new ratio asks of the other: kerosene : diesel = 4 : 6 means diesel = 6⁄4 of the kerosene.

In ratio parts: kerosene stays at 4 parts while diesel goes from 5 to 6, so add 1 part = 5 L.

The target 4 : 6 is 2 : 3 in lowest terms. Left as 4 : 6, it lines up with 4 : 5, since kerosene is 4 parts in both.

Key facts

In a ratio a : b with total T, one part = T ÷ (a + b).
Adding only one component leaves the other unchanged, so work from the unchanged one.
4 : 6 and 2 : 3 are the same ratio.

Study next

Replacement: drawing off part of a mixture and refilling with one liquidMixing two solutions of different strengths by alligationAdding one component to reach a target percentage

Common traps

Applying 4 : 6 to the old 45 L: that puts kerosene at 18 L, but no kerosene was removed.
Answering with the new diesel total, 30 L, instead of the amount added, 30 − 25 = 5 L.

Adding one liquid to reach a new ratio also appears at 12 Sep 2025, 09:00, Quant Q.15, where 40 L of juice and water at 5 : 3 needs 22.5 L of water to reach 2 : 3.

23 Sep 2024, 09:00, Quant Q.20 sets the target as a percentage: 8 L of water takes a 32 L milk-water mix at 5 : 3 to 50% water.

Related PYQs

No directly related past PYQ was found.

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