ISRO EC 2025 Q.85: solution and answer

ISRO 2025 · ECQ.85 · 1 mark · MCQ

In a mixture of 45 litres, the ratio of sugar solution to salt solution is 1 : 2. What is the amount of sugar solution to be added if the ratio has to be 2 : 1?

(A)
15 litres
(B)
45 litres
(C)
55 litres
(D)
65 litres

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Answer and solution

ANSWER

The amount of sugar solution to be added is $45$ litres, which is option (b).

Official answer: BSource: ISRO's final answer key of 15 May 2026

Split the $45$ litres in the ratio $1 : 2$ : sugar solution $= \frac{1}{3} \times 45 = 15$ litres and salt solution $= \frac{2}{3} \times 45 = 30$ litres.
Only sugar solution is added, so the salt solution stays at $30$ litres.
Let $x$ litres of sugar solution be added. The new ratio must be $\frac{15 + x}{30} = \frac{2}{1}$ .
So $15 + x = 60$ , which gives $x = 45$ litres.
Check: sugar $= 60$ litres and salt $= 30$ litres, so the ratio is $60 : 30 = 2 : 1$ .
The other options fail. Adding $15$ litres gives $30 : 30 = 1 : 1$ . Adding $55$ litres gives $70 : 30$ . Adding $65$ litres gives $80 : 30$ . None of these equals $2 : 1$ .

KEY IDEA

When only one component is added, the other component's quantity stays fixed. Use it as the anchor and set up the new ratio against it.

WATCH OUT FOR

Treating the new total as $45$ litres and splitting it $2 : 1$ (giving $30$ litres of sugar and so adding $15$ ), or forgetting that the salt solution stays at $30$ litres while only the sugar solution changes.

From the ISRO EC 2025 paper. Also Q.85 of the ISRO Scientist/Engineer Computer Science 2025 paper. Every question of this paper · The full paper (PDF, ISRO) · All 5 ISRO Numerical questions, with notes

ISRO EC 2025 Q.85: solution and answer

Answer and solution

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