Question 107435
The sum of their rates of painting is the rate of all three
together
(1 house/2 hrs) + (1 house/4 hrs) + (1 house/8 hours) = (1 house)/x hours)
1/2 + 1/4 + 1/8 = 1/x
4/8 + 2/8 + 1/8 = 1/x
7/8 = 1/x
x = 8/7
So, working together, they take 1 hour 8.5 minutes approx