It took Matt twice the time to drive from home to work as it took him to drive back home from work by the same route.If Matt averaged 30 miles per hour on his drive to work,how was his average speed for the entire round trip?
A. 30 mph
B. 25 mph
C. 40 mph
D. 15 mph

Question

It took Matt twice the time to drive from home to work as it took him to drive back home from work by the same route.If Matt averaged 30 miles per hour on his drive to work,how was his average speed for the entire round trip?
A. 30 mph
B. 25 mph
C. 40 mph
D. 15 mph

phi · Answer

home to work:   2T hours at 30 mph
work to home:   T hours at unknown speed

use 
rate*time= distance
2T*30= d  
d= 60T  this is the distance from home to work
2d is the round-trip distance

phi · Answer

average speed for the entire round trip?

average speed is  total distance / total time
total distance is 2d= 120T
total time is 2T+T= 3T
average speed is
$$ \frac{120T}{3T}= 40 $$