Question 870445
it takes 1/20 of an hour to go 1 km at 20 kmh
it takes 1/50 of an hour to go 1 km at 50 kmh
r*t=d
r=d/t
average speed is total distance /total time
add d=1 +1
add t=1/20+1/50
d/t=
28.57 kph average speed