How much of a mixture to draw off and replace to reach a target ratio

This type of question, asked 2 times: 26 Jul 2023 S1, 12 Sep 2025 S2. All 2 questions below, oldest first.

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Question 1
26 Jul 2023 S1
51 $A vessel is filled with liquid, 5 parts of which are water and 11 parts syrup. What part of the mixture must be drawn off and replaced with water so that the mixture may be syrup and water in the ratio 3 : 2?$
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Question 2
12 Sep 2025 S2
63 $A 100-litre solution contains acid and water in the ratio 3:2. Some quantity of this solution is removed and replaced with pure acid. If the final ratio of acid to water becomes 7:3, how many litres of solution were replaced?$
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Question 1