Difficulty: Hard
Correct Answer: 7:5
Explanation:
Introduction / Context:This problem tests mixing two mixtures to achieve a target concentration (here, 50% milk). The correct approach is to use milk fractions (or alligation) and solve for the mixing ratio between the two vessels. Since the vessels have different milk percentages, the final mixture percentage depends on how much is taken from each.
Given Data / Assumptions:
Concept / Approach:Convert each vessel ratio to milk fraction. Set combined milk fraction to 1/2 and solve for x:y.
Step-by-Step Solution:
Step 1: Milk fraction in A = 4/(4+3) = 4/7 Step 2: Milk fraction in B = 2/(2+3) = 2/5 Step 3: Let x units from A and y units from B be mixed Step 4: Total milk = x*(4/7) + y*(2/5) Step 5: Total mixture volume = x + y Step 6: Target condition: [x*(4/7) + y*(2/5)] / (x + y) = 1/2 Step 7: Multiply by 2(x+y): 2*(4x/7 + 2y/5) = x + y Step 8: 8x/7 + 4y/5 = x + y Step 9: (8/7 - 1)x + (4/5 - 1)y = 0 => (1/7)x - (1/5)y = 0 Step 10: x/7 = y/5 => x:y = 7:5Verification / Alternative check:Mix 7 L from A and 5 L from B. Milk = 7*(4/7)=4 plus 5*(2/5)=2 total 6. Total volume = 12, so milk% = 6/12 = 50%. Verified.
Why Other Options Are Wrong:
5:7: inverted ratio gives milk% different from 50%. 6:7, 11:7, 8:3: these do not satisfy the equation that milk equals half of total.Common Pitfalls:People often mix ratios 4:3 and 2:3 directly or take a naive average. Always convert to milk fractions (4/7 and 2/5) first. Another error is mixing up A:B vs B:A.
Final Answer:7:5
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