If 9 workers finish a task in 13 days, how many days will 18 equal workers need?

Question: If 9 workers finish a task in 13 days, how many days will 18 equal workers need?

1. 7 days
2. 6 days
3. 15/2 days
4. 13/2 days

Correct Answer: D — 13/2 days

Explanation: For the same job, workers × time stays constant when rates are equal.
Using the values in this question gives 13/2 days as the correct answer.