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QUANTITATIVE REASONING · GMAT-Q-MX-01
Mixtures and Concentration
GMAT lesson development preview · DRAFT · Original learning and assessment material
Concepts and problem-solving strategy
Think Like a GMAT Test-Taker
Track the absolute amount of pure ingredient, then divide by total volume.
Faster Methods
Use weighted concentration, not average of percentages unless volumes are equal.
Check the target lies between input concentrations.
Worked example 1
Mix 2 L of 10% solution and 3 L of 20%. Find concentration.
Total solute is 0.8 L; mixture is 5 L, thus 16%.
Worked example 2
How much water must be added to 4 L of 30% solution to obtain 20%?
Solute stays 1.2 L, so total volume must become 6 L.
Common Traps
- Percentages describe a fraction of each mixture, not an absolute amount.
- Adding water changes total volume but not the solute amount.