GMAT Focus EditionQuantitative ReasoningMedium
A chemist needs to create 10 liters of a 40% acid solution. She has two solutions available: Solution A, which is 25% acid, and Solution B, which is 50% acid. How many liters of Solution A must she use?
- A6 liters
- B4 liters
- C7 liters
- D3 liters
Show answer & explanationAnswer & explanation
Correct answer: B. 4 liters
Let 'x' be the liters of Solution A and 'y' be the liters of Solution B. We have x + y = 10 and 0.25x + 0.50y = 0.40 * 10. Solving these simultaneous equations yields x = 4 liters.
Why the other options are wrong
- A. This is incorrect; it might be the amount of Solution B if calculated incorrectly.
- C. This is incorrect; it might result from an algebraic error or miscalculation of the final total acid.
- D. This is incorrect; it might result from an algebraic error in solving the system.
Mixture Problems (Algebraic)
Problems involving combining two or more substances with different concentrations to achieve a desired final concentration or quantity.
- Set up equations for total quantity and total amount of solute.
- Often involves solving a system of two linear equations.
- Concentration is (amount of solute / total quantity).
Memory trick: Two equations, two unknowns, total volume and total 'stuff' combine.