#### Answer

$\frac{520}{1440}$ = $\frac{13}{36}$

#### Work Step by Step

First we need to calculate the total number of minutes in a day,
As in 1 day there are 24 hours and in each hour there are 60 min so total number of minutes in a day are = 24 * 60 = 1440 min
People are spending 8 hours 40 minutes on sleeping So we need to calculate the minutes on sleeping = 8 * 60 + 40 min = 480 min + 40 min= 520 min
Americans spend how much time sleeping compared to the total number of minutes in a day = $\frac{520}{1440}$ = $\frac{13}{36}$