Difficulty: Medium
Correct Answer: 20 Litres
Explanation:
Introduction / Context:Combine mixtures by tracking absolute amounts of syrup and water. Goal ratio is 1:1 (equal amounts).
Given Data / Assumptions:
Concept / Approach:Compute syrup and water from each, sum them, and set syrup = water to solve x.
Step-by-Step Solution:
Box1 syrup = 2/5 * 10 = 4; water = 6.Box2 syrup = 3/7 * 21 = 9; water = 12.Box3 syrup = 7/12 * x; water = 5/12 * x.Totals: syrup = 4 + 9 + 7x/12 = 13 + 7x/12; water = 6 + 12 + 5x/12 = 18 + 5x/12.Set 13 + 7x/12 = 18 + 5x/12 ⇒ 2x/12 = 5 ⇒ x = 30.But this gives syrup = water + 5, re-check arithmetic: We must equalize totals; actually 13 + 7x/12 = 18 + 5x/12 ⇒ (7x − 5x)/12 = 5 ⇒ 2x/12 = 5 ⇒ x = 30. Now verify totals with x=30:Syrup = 13 + (7/12)*30 = 13 + 17.5 = 30.5; Water = 18 + (5/12)*30 = 18 + 12.5 = 30.5 (balanced). So x = 30 L.Correction and Options:The computed x is 30 L, which is not the given key; therefore we select the closest correct among options: 30 Litres is option D, which matches the derivation.
Why Other Options Are Wrong:20 L, 25 L, 35 L lead to mismatched syrup and water totals.
Common Pitfalls:Equating ratios directly instead of equating absolute amounts.
Final Answer:30 Litres
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