Question

Round the answer by the nearest hundred.Working alone, Mark can tar a roof in 9 hours. Ashley can tar the same roof in 15 hours. How long would it take them if they worked together?

Answer 1

Given:

`\begin{gathered} Mark(tar-a-roof)=9hours \\ Ashley(tar-a-roof)=15hours \end{gathered}`

To determine: How long it will take Mark and Ashley to a roof

Solution

Let us determine the unit of roof tar by Mark and Ashley in one hour

`\begin{gathered} Mark(unit-tar-in-1hour)=(1)/(9) \\ Ashley(unit-tarred-in-1hour)=(1)/(15) \\ Mark&Ashley(unit-tarred-in-1hour)=(1)/(9)+(1)/(15)=(5+3)/(45)=(8)/(45) \end{gathered}`

Therefore, the time it will take them to tar a roof would be as calculated below if it took them x hours

`\begin{gathered} (8)/(45)* x=1 \\ (8x)/(45)=1 \\ 8x=45 \\ x=(45)/(8) \\ x=5.625 \\ x=5.63hours \end{gathered}`

Hence, it will take both of them approximately 5.63 hours to tar the roof