A boy can rake a yard in 2.5 hours, his sister can rake it in 4 hours. How long will it take both of them to rake it?

Answer 1

Reiny answered this.

http://www.jiskha.com/display.cgi?id=1349221382

Answer 2

In 40 hours, he can rake 16 yards, she can rake 10, so both can rake 26 in 40 hours, or rate=25/40 yards/hr. Reduce that fraction to a decimal.