Question

Jack and Serena can write a lab report together in $6$ hours. If all people work at the same rate, how many hours would it take to write a lab report if Kay joins Jack and Serena?

Answer 1

4 hours

Explanation:

The number of people and the amount of time needed are inversely proportional.

So, when Kay joins to help, there are 3/2 as many people as there were before, so since Jack and Serena can finish the report in 6 hours, we multiply 2/3, the reciprocal of 3/2, with 6 to get 4 hours.

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Answer 2

4 hours

Explanation:

If all work at the same rate, the time required is inversely proportional to the number of people on task. If the number of writers goes from 2 to 3 (is multiplied by 3/2), the time required will be 2/3 of that for 2 people:

(2/3)(6 hours) = 4 hours

If Kay joins Jack and Serena, the lab report can be done in 4 hours.