Question

If Jim Roller can paint a room in 3 hours while John Brush would take 5 hours, how long will they take if they work together?

A. 1/8 hour

B. 8/15 hour

C. 1 7/8 hours

Answer 1

C. 17/8 hr

Each hour , Jim does 1/3 of the job if working alone.
Each hour, John does 1/5 of the job if working alone.

Let x = number of hours to do the job if they work together. So, each hour, they do 1/x of the job when they work together.

We get the equation: 1/3 + 1/5 = 1/x

Multiply the equation by the LCD, 15x:
5x + 3x = 15

8x = 15

x = 15/8 = 1 7/8 hrs