GMAT Focus EditionQuantitative ReasoningMedium
A project manager estimates that a task can be completed by 3 workers in 15 days. If the manager needs the task completed in 9 days, how many additional workers, with the same work rate, are required?
- A3
- B5
- C2
- D4
Show answer & explanationAnswer & explanation
Correct answer: C. 2
This is an inverse proportion problem. The total 'worker-days' needed is 3 workers * 15 days = 45 worker-days. To complete the task in 9 days, you need 45 worker-days / 9 days = 5 workers. Since there are already 3 workers, 5 - 3 = 2 additional workers are needed.
Why the other options are wrong
- A. Incorrect. This would mean 6 total workers, which would complete the task in 7.5 days.
- B. Incorrect. This would mean 8 total workers, completing the task significantly faster.
- D. Incorrect. This would mean 7 total workers, completing the task even faster.
Inverse Proportion
A relationship between two quantities where an increase in one leads to a decrease in the other, such that their product remains constant.
- Example: More workers means less time to complete a task.
- Formula: x1*y1 = x2*y2
- Often seen in 'work rate' problems.
Memory trick: Proportions link numbers, direct or inverse, they show how things stir.