1. Suppose his home is one kilometer from school, then1/3 * a/+2/3 * a/20 = a/5-15/60 gets a=2.5 kilometers.

2. Let the plane speed be one kilometer per hour, then 5.5(24+a)=6(a-24), and a= 552 kilometers per hour.

Then the distance between the two cities is 6 (a-24) = 3 168km.

3。 Let the train length be x, then x =1000/60 = (1000-x)/40 is 1000/3m.