John can paint 60 walls in 20 minutes. Emma can paint 9 walls in 15 minutes. Working together, how many walls can they paint in 25 minutes?

Question: John can paint 60 walls in 20 minutes. Emma can paint 9 walls in 15 minutes. Working together, how many walls can they paint in 25 minutes?

Solution:
John can paint in 1 min = 60/20 = 3 walls
Emma can paint in 1 min = 9/15 = 3/5 walls

∴ Working together they can paint in 1 min = (3 + 3/5) = 18/5 walls

∴ They can paint in 25 min = (18 × 25)/5 = 90 walls

So John and Emma can paint 90 walls together in 25 minutes.