It takes 20 minutes for5 people to paint 5walls. How many minutes does it take 9 people to paint 9 walls?

Answer 1

Assume that 1 wall is 900 ft². (This is an arbitrary number, any reasonable number can be used)

So, 5 walls = 4500 ft² & since there are 5 people (all doing equal work) then each man paints 900 ft² in 20 minutes.

For 9 walls, there is 8100 ft², with 9 people, each person paints 900 ft² but we know from above that it takes 20 minutes for each man to paint 900 ft²

So, the total time is 20 minutes.