Question

To collect data on the signal strengths in a neighborhood, Briana must drive from house to house

and take readings. She has a graduate student, Henry, to assist her. Briana figures it would take her
12 hours to complete the task working alone, and that it would take Henry 18 hours if he completed
the task by himself.

Answer 1

Answer: Working together, they can complete the task in 7 hours and 12 minutes.

Explanation:

Ok, Briana needs 12 hours to complete the task.

Then we can find the ratio of work over time as:

1 task/12hours = 1/12 task per hour.

This means that she can complete 1/12 of the task per hour.

Henry needs 18 hours to complete the task, then his ratio is:

1 task/18 hours = 1/18 task per hour.

This means that he can complete 1/18 of the task in one hour.

If they work together, then the ratios can be added:

R = 1/12 + 1/18 = 18/(12*18) + 12/(18*12) = 30/216

we can reduce it to:

R = 15/108 = 5/36

So, working together, in one hour they can complete 5/36 of the task, now we can find the number of hours needed to complete the task as:

(5/36)*x = 1 task

x = 36/5 hours = 7.2 hours

knowing that an hour is 60 minutes, then 0.2 of an hour is 60*0.2 = 12 minutes.

then x = 7 hours and 12 minutes.