Question

Josh can paint a whole room in m hours while Kevin can paint a whole room in n hours. How many parts of the room can they paint in one hour if both of them worked together? Express in terms of m and n.​

Answer 1

Answer: (m+n)/(mn)

Work Shown:

Josh:

1 room = m hours

1/m room = 1 hour

Kevin:

1 room = n hours

1/n room = 1 hour

We see that the rates for Josh and Kevin are 1/m and 1/n respectively. This is the amount of a room they paint in one hour. Combine the fractions

1/m + 1/n = n/(mn) + m/(mn) = (n+m)/(mn) = (m+n)/(mn)

The expression (m+n)/(mn) represents how much of the room they get painted in 1 hour. This is if they work together and it assumes neither worker slows the other one down.