Problem:
If you walk for 45 minutes at a rate of 4mph and then run for 30 minutes at a rate of, 10mph, how many miles have you gone at the end of one hour and 15 minutes?
Answer Choices:
A. 3.5 miles
B. 8 miles
C. 9 miles
D. 2531​ miles
E. 480 miles
Solution:
To keep the units of miles and hours, first note 45 minutes =6045​=43​ hour and 30 minutes =21​ hour. Since distance = rate × time, your total distance is
4×43​+10×21​=3+5=8 miles.
The distance is less than 4+10=14 miles, so (D) and (E) can be easily eliminated.
Answer: B​.
The problems on this page are the property of the MAA's American Mathematics Competitions