Problema Solution
Christopher can paint the interior of his house in 15 hours. If he hires Cynthia to help him, they can do the same job together in 9 hours. If he lets Cynthia work alone, how long will it take her to paint the interior of his house?
Answer provided by our tutors
time for cynthia alone = c
9/15 + 9/c = 1
0.6 + 9/c = 1
9/c = 0.4
c = 9/0.4
c = 22.5 hours to do alone