If it takes Mr. Sunday 4 hours to paint a house, and it takes Mr. Armstrong 5 hours to paint the same house. How long will it take for them to paint the house together?

Answer 1

Let's assume the house is 1000 ft² (This is an arbitrary number, any reasonable will be OK)

Then, Mr. Sunday takes 4 hours to paint 1000 ft² or he can paint 1000 ft²/4 hours or 250 ft²/hour

Then, Mr. Armstrong takes 5 hours to paint 1000 ft² or he can paint 1000ft²/5 hours = 200 ft²/hour

So, both working together they can paint 450 ft²/hour, So, 1000 ft²/(450 ft²/hour) = 2.22 hours

So, working together, it takes them about 2 hours and 13 minutes!