Average speed

Question

A truck driver traveled at an average speed of 55 miles per hour on a 200- mile trip with the truck fully loaded. The average speed was 40 miles per hour. What was the average speed for the round trip?

Answer 1

Do you mean 55 mph with the truck loaded and 40 mph back with the truck unloaded ?

If so,...

distance=rate*time

200=55*t

t=200/55

t=3 35/55=3 7/11 hours up

 

200=40*t

t=200/40

t=5 hours back

 

total distance=rate*total time

400=rate*(8 7/11)

400=rate*(95/11)

(11/95)(400)=rate*(11/95)(95/11)

(11*400/95)=rate

4400/95=rate

rate=46.315789 mph average speed for the round trip

 

if you know what the harmonic mean is you can solve the problem this way...

(2*55*40)/(55+40)

4400/95=46.315789 mph again