Two bikes are moving with speeds m km/h and n km/h towards a crossing along two perpendicular roads. If their distances from the crossing be 60 meters and 70 meters respectively at an instant of time then they do not collide if their speeds are such that
1
m : n ≠ 6 : 7
2
m : n ≠ 7 : 6
3
m : n ≠ 36 : 49
4
m : n ≠ 12 : 14