Then the return journey is just the opposite, the downhill part becomes uphill and the uphill part becomes downhill.
Then: a round trip is equivalent to * * * uphill 48KM and downhill 48 km.
You can draw a picture to make it clearer.
So:
48÷8+48÷ downhill average speed =2.5+4.8.
48÷ downhill average speed =2.5+4.8-48÷8
Average downhill speed = 48(2.5+4.8-48÷8)
=48÷ 1.3=480/ 13 =36 12/ 13
About 37 kilometers per hour
Students in the fourth grade should be able to understand the problem in this way.