2010 AMC 10A Problem 13

Angelina drove at an average rate of 80 km/h and then stopped 20 minutes for gas. After the stop, she drove at an average rate of 100 km/h. Altogether she drove 250 km in a total trip time of 3 hours including the stop. Which equation could be used to solve for the time t in hours that she drove before her stop?

\mathrm{(A)}\ 80t + 100\left(\frac{8}{3} -t\right) = 250 \qquad \mathrm{(B)}\ 80t = 250 \qquad \mathrm{(C)}\ 100t = 250
\mathrm{(D)}\ 90t = 250 \qquad \mathrm{(E)}\ 80\left(\frac{8}{3} -t\right) + 100t = 250

Full credit goes to MAA for authoring these problems. These problems were taken on the AOPS website.