GRE General TestQuantitative ReasoningMedium
A chemist is preparing a solution. She needs to mix 3 parts of chemical A with 5 parts of chemical B. If she uses 120 mL of chemical A, how much chemical B (in mL) does she need?
- A120 mL
- B72 mL
- C200 mL
- D320 mL
Show answer & explanationAnswer & explanation
Correct answer: C. 200 mL
Set up a proportion: (parts of A) / (volume of A) = (parts of B) / (volume of B). Solve for the unknown volume of B.
Why the other options are wrong
- A. This assumes equal parts, which is incorrect based on the ratio.
- B. This would be the amount if the ratio was 5 parts A to 3 parts B.
- D. This error likely added the parts (3+5=8) and then multiplied 8 by 120 or similar miscalculation.
Proportional Reasoning
Proportional reasoning involves understanding how quantities change in relation to each other, often expressed as ratios or fractions.
- Ratios compare two quantities.
- Proportions state that two ratios are equal.
- Can be used to find an unknown quantity when other parts are known.
Memory trick: Ratio's Rule: Set up fractions, cross-multiply, and solve!