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 has 480 milliliters of chemical B, how many milliliters of chemical A does she need?
- A288 mL
- B240 mL
- C300 mL
- D180 mL
Show answer & explanationAnswer & explanation
Correct answer: A. 288 mL
The ratio of Chemical A to Chemical B is 3:5. Let 'x' be the amount of Chemical A. Set up the proportion: 3/5 = x/480. Cross-multiply: 5x = 3 * 480. 5x = 1440. x = 1440 / 5 = 288 mL.
Why the other options are wrong
- B. This would be the answer if the ratio was 1:2 (A to B) or 1:1 if 480 was total.
- C. This would be the amount if the ratio was 5:8, or other incorrect ratio setup.
- D. This is incorrect; it's a plausible distractor from miscalculation.
Proportional Reasoning
Proportional reasoning involves understanding and applying relationships where two ratios are equivalent. It's used to find unknown quantities when a known ratio is given.
- A proportion is an equation stating that two ratios are equal.
- If a/b = c/d, then ad = bc (cross-multiplication).
- Identify the corresponding parts of the ratio and quantities.
Memory trick: Cross-multiply to find the missing piece.