## Algebra: A Combined Approach (4th Edition)

It takes them $\frac{20}{9}$ days.
Rate is given by jobs completed divided by the time it took to do those jobs. Mr. Dodsons rate →$R_{D}$ Mr. Dodson's son's rate →$R_{S}$ How long it takes to paint the house→J Mr.Dodson can paint a house by himself in 4 days so his rate is $\frac{1}{4}$. His son can paint a house by himself in 5 days so his rate is $\frac{1}{5}$. $R_{D}$T+$R_{S}$T=J $\frac{1}{4}$T+$\frac{1}{5}$T=1 $\frac{9}{20}$T=1 T=$\frac{20}{9}$