Problem:
Angelina drove at an average rate of 80kph and then stopped 20 minutes for gas. After the stop, she drove at an average rate of 100kph. 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?
Answer Choices:
A. 80t+100(8/3−t)=250
B. 80t=250
C. 100t=250
D. 90t=250
E. 80(8/3−t)+100t=250
Solution:
Angelina drove 80t km before she stopped. After her stop, she drove (3−31​−t) hours at an average rate of 100kph, so she covered 100(38​−t) km in that time. Therefore (A)80t+100(38​−t)=250​. Note that t=65​.
The problems on this page are the property of the MAA's American Mathematics Competitions