If a train goes whit ...mph towards you and your train is moving at ...kmph (to make it harder), when will the trains collide?
if train a is moving with s1 kmph and train b with s2 mph and they are d distance apart and the conversion factor from kmph to mph is c, then...(c*s1 - s2)/d
Very young child (we call it a baby): Tjoo Tjoo
I think I still have a Legotrain in my room. Doesn't work, but that 's an other thing.