Maths Problem 4

Question

4. A truck driver travels a certain distance at 60 km/hour per hour and returns over the same distance at 40 km/hour. What is her average speed for the entire trip?

Answer 1

the distance traveled does not matter because they are the same coming and going

let's choose 120 miles for our distance

d=r*t

120=60*t (going)

t=2 hours

120=40*t (returning)

t=3 hours

total distance=rate*total time

(120+120)=rate*(2+3)

240=rate*5

rate=240/5

rate=48 km per hour

if you are familiar with the harmonic mean, you can get the answer that way...

(2*60*40)/(60+40)=4800/100=48 again