Three trains A , B and C having speeds 50 km/hr , 20 km/hr and 70 km/hr respectively, if A and C move towards East and B moves towards west, then the ratio of relative speed of train A and B to the relative speed of train B and C?
1
5 : 9
2
9 : 7
3
5 : 2
4
7 : 9
5
4 : 5