Help calculate average speed

Question

suppose that on an 80 mile trip, you average 20 mph on the first 5 miles, and on the remaining 75 miles you average 75 mph. Remembering that speed is found by taking distance divided by time, what is your average speed for the entire trip

Answer 1

d=rt

5=20t

t=5/20=1/4 hour

75=75t

t=75/75=1 hour

total distance=rate*total time

80=rate*1.25

rate=80/1.25

rate=64 mph is the average speed

Answer 2

distance = rate x time

distance/rate = time

 

(5 miles)/(20 mph) = 0.25 hours

(75 miles)/(75 mph) = 1 hour

 

Total time = 0.25 hour + 1 hour = 1.25 hours

Total distance = 5 miles + 75 miles = 80 miles

 

distance = rate x time

distance/time = rate

(80 miles)/(1.25 hours) = _____