A mixture contains 12 litres of 30% acid solution.
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A mixture contains 12 litres of 30% acid solution. How much 20% acid solution should be added to make it 25% acid?
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Answer: B. B) 12 litres
By the rule of alligation, mixing 30% and 20% to achieve 25% requires equal proportions (1:1). Adding 12 litres of 20% solution yields the 25% concentration.
Step-by-step Derivation:
Step 1: Alligation ratio: (30 - 25) : (25 - 20) = 5 : 5 = 1 : 1.
Step 2: Since initial volume of 30% acid is 12 litres, exactly 12 litres of 20% acid must be added.