Could someone help me with this please:
Two trains, both 200 metres long, travel on parallel tracks through a tunnel. One travels at 100 KM/h, the other at 200 KM/h. The front of the fast train enters the tunnel just as it passes the back of the slow train. The back of the fast train leaves the tunnel just as it passes the front of the slow train. How long is the tunnel?
Thanks for taking a look!