Xiaojie and Xiaoli set out from school at the same time and walked 15km to the county seat to buy books. Xiaojie walks 1km more than Xiaoli every hour. As a result, they arrive half an hour earlier than Xiaoli. How long did it take Xiaojie and Xiaoli to get to the county seat?

Let Xiaojie's speed be x km/h.

15/(x- 1)- 15/x = 0.5

15x- 15(x- 1)= 0.5x(x- 1)

x？ -x-30=0

(x-6)(x+5)=0

x=6

X=-5 (uncorrelated)

Xiaojie 15÷6=2.5 hours

Xiao Li 15(6- 1)= 3 hours.