AlgebraVery hardWater added to dilute a solution
Algebra practice question
A 200-millilitre solution is 15 percent salt. How many millilitres of pure water must be added so that the solution becomes 10 percent salt?
Answer: 100
The salt stays at 30 millilitres, so 30 = 0.10(200 + w) gives w = 100.
Common wrong answers
- If you answered 20
- 20 uses 10 percent of 200.
- If you answered 50
- 50 uses 30 = 0.10(200 + w) with a division slip.
- If you answered 300
- 300 is the final volume, not the water added.
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