tong van toc 2 xe la:
40 + 30 = 70km/h
2 xe gap nhau sau:
140 : 70 = 2 gio
2 xe gap nhau luc:
7 + 2 = 9 gio
dia diem gap cach cho khoi hanh cua xe may la:
30 x 2 = 60km
dia diem gap cach cho khoi hanh cua xe o to la:
40 x 2 = 80km
dap so
9 gio
60km
80 km