The quality of water that should be added to reduce 9 ml. Lotion containing 50 % alcohol to a lotion containing 30 % alcohol is_________?
Correct answer: D. 6 ml
- A. 3 ml
- B. 4 ml
- C. 5 ml
- D. 6 ml
Explanation
The 9 ml lotion contains 9 ml × 50% = 4.5 ml alcohol. For this 4.5 ml alcohol to be 30% of the final mixture, the final volume must be 4.5 ml ÷ 0.30 = 15 ml, so water added is 15 ml − 9 ml = 6 ml. A student may choose c, 5 ml, by treating the original 50% concentration as if it were already the required final concentration.
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