John can paint a wall in 30 minutes. James can paint that same wall in 20 minutes.How long would it take them if they worked together?

Question

John can paint a wall in 30 minutes. James can paint that same wall in 20 minutes.How long would it take them if they worked together?

Answer 1

John can paint 1/30 of a wall in 1 minute.

 

James can paint 1/20 of a wall in 1 minute.

 

So if they work together, they can both paint 1/30 + 1/20 of a wall in 1 minute.

 

1/30 + 1/20 = 2/60 + 3/60 = 5/60 = 1/12.

 

So together they can paint 1/12 of a wall in 1 minute.  So they can paint the entire wall in 12 minutes.