Jeff takes 20 minutes to jog around the race course one time, and 25 minutes to jog around a second time. what is his average speed in miles per hour for the whole jog if the course is 3 miles long?
a. 6
b. 8
c. 10
d. 12
e. 14

Distance = rate*time 
distance/time = rate

The race course is 3 miles around and Jeff does it twice, so the distance he goes = 2*3 miles = 6 miles. 

 He takes 20 minutes to go around once and 25 minutes to go around the second time, so the total time = 20 min + 25 min = 45 min. 

His speed is miles per hour, not miles per minute, so convert 45 minutes to a hours:
 45 min/60 min = 0.75 hours distance/time = rate = 6 miles/0.75 hours = 8 mph