729 ml of a mixture contains milk and water in the ratio 7:2. How much of the…
2023
729 ml of a mixture contains milk and water in the ratio 7:2. How much of the water is to be added to get a new mixture containing half milk and half water ?
Answer: B. 405 ml — Concept: In a mixture, only the ingredient being added changes; every other ingredient's quantity stays fixed. So to make two ingredients equal by adding only…
- A.
81 ml
- B.
405 ml
- C.
972 ml
- D.
910 ml
Attempted by 28 students.
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Correct answer: B
Concept: In a mixture, only the ingredient being added changes; every other ingredient's quantity stays fixed. So to make two ingredients equal by adding only one of them, raise that ingredient up to match the quantity of the ingredient that isn't being touched -- the required addition is simply that difference.
Split the 729 ml mixture in the ratio 7:2 (total 9 parts): milk = 729 x 7/9 = 567 ml.
Water = 729 - 567 = 162 ml (equivalently 729 x 2/9).
Only water is being added, so milk remains fixed at 567 ml. For the final mixture to be half milk and half water, water must also equal 567 ml.
Water to be added = 567 - 162 = 405 ml.
Cross-check: after adding 405 ml of water, the mixture has 567 ml milk and 162 + 405 = 567 ml water -- an equal 1:1 split, confirming the answer.
So 405 ml of water must be added.