AlgebraVery hardMixture of two solutions
Algebra practice question
A chemist mixes a 50% acid solution with an 80% acid solution to make 60 millilitres of a 60% acid solution. How many millilitres of the 80% solution are used?
Answer: 20
Let a be the millilitres of 50% solution and b of 80%: a + b = 60 and 0.5a + 0.8b = 0.6(60) = 36. Substituting a = 60 − b: 30 − 0.5b + 0.8b = 36 → 0.3b = 6 → b = 20.
Common wrong answers
- If you answered 30
- 30 assumes equal amounts, which would give 65%, not 60%.
- If you answered 36
- 36 is the millilitres of pure acid in the mixture, not of the 80% solution.
- If you answered 40
- 40 is the amount of the 50% solution.
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