Question

Christopher can paint the interior of his house in 27 hours. If he hires Cynthia to help him they can do the same job together in 21 hours. If he lets Cynthia work alone, how long will it take her to paint the interior of his house?

Answer 1

Cynthia alone will take `94.5` hour to paint interior of house.

Explanation:

In `1` hour Christopher paints `1/27` part of work

In `1` hour Christopher and Cynthia paint `1/21` part of same

work. Therefore, In `1` hour Cynthia paints

`(1/21-1/27)=(9-7)/189=2/189` part of same work

So Cynthia alone can paint same work in `1-:(2/189)=189/2`

`=94.5` hour.

Cynthia alone will take `94.5` hour to paint interior of house. [Ans]