GMAT Focus EditionQuantitative ReasoningEasy
A project team is planning to complete a task. If 3 engineers can complete the task in 12 days, how many days will it take for 9 engineers to complete the same task, assuming they work at the same rate?
- A3 days
- B8 days
- C4 days
- D6 days
Show answer & explanationAnswer & explanation
Correct answer: C. 4 days
This is an inverse proportion problem: as the number of engineers increases, the time taken to complete the task decreases. The total work is constant (Engineers * Days). So, 3 engineers * 12 days = 9 engineers * X days. X = (3 * 12) / 9 = 36 / 9 = 4 days.
Why the other options are wrong
- A. This would be 36/12 not 36/9.
- B. Incorrect calculation.
- D. Incorrect calculation.
Inverse Proportion
Two quantities are in inverse proportion if their product is a constant. As one quantity increases, the other decreases proportionally (y = k/x or xy = k).
- Often seen in work-rate problems (more workers, less time).
- The relationship is xy = k, where k is the constant of proportionality.
- Can be solved by setting up two scenarios equal to the constant.
Memory trick: Inverse means Product Stays Constant.