A janitor cleans 3 classrooms in 1.5 hours. He gets a new wing with 9 classrooms. If he hires help with 80% his speed, how long will they take?
Correct answer: A. 2.5 hrs
- A. 2.5 hrs
- B. 3 hrs
- C. 3.5 hrs
- D. 4 hrs
Explanation
The janitor cleans 3 classrooms in 1.5 hours, which means his cleaning rate is 2 classrooms per hour. The helper, working at 80% of the janitor's speed, cleans 1.6 classrooms per hour. Together, their combined rate is 2 + 1.6 = 3.6 classrooms per hour. To clean 9 classrooms, they will need 9 / 3.6 = 2.5 hours. Therefore, the correct option is2.5 hrs. Options B, C, and D are incorrect as they all overestimate the time required due to miscalculations of the combined work rate.
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