Solve the problem.
-Amy can clean the house in 9 hours. When she works together with Tom, the job takes 4 hours. How long would it take Tom, working by himself, to clean the house?
A) 5 hours
B) $8 \frac { 1 } { 5 }$ hours
C) $7 \frac { 2 } { 5 }$ hours
D) $7 \frac { 1 } { 5 }$ hours

Question

Quizplus · Accepted Answer

Let's assume that Tom can clean the house in x hours working alone.

Amy can clean the house in 9 hours, so in one hour, she can do 1/9 of the job.

When they work together, the job takes 4 hours. So, in one hour, they can do 1/4 of the job working together.

We can set up the following equation:

1/9 + 1/x = 1/4

Multiplying both sides by 36x gives:

4x + 36 = 9x

5x = 36

x = 7.2

So, Tom can clean the house by himself in 7.2 hours which is equal to $7 \frac { 1 } { 5 }$ hours.

Therefore, the answer is D.

Solve the Problem 8158 \frac { 1 } { 5 }851​

Solve the Problem $8 \frac { 1 } { 5 }$