Xiaoding went to Zhou Xiao's home by bike. He first went down the mountain at a speed of 12km/h, and then walked a flat road at a speed of 9km, which took 55 minutes to hang up.

It's more troublesome to use one dollar at a time.

55 minutes =1112 hours.

Suppose that the downhill from Xiaoding's house to Zhouxiao's house is X kilometers.

( 1 1/ 12-x/ 12)* 9 =( 1.5-x/4)* 8

33/4-3/4*x= 12-2x

5/4*x= 12-33/4

5x=48-33

5x= 15

X=3 kilometers

The horizontal road is: (1.5-3/4) * 8 = (1.5-3/4) * 8 = 6 km.

So the distance between Xiaodinggu and Zhouxiaogu is:

3+6=9 km