A knight wanted to visit a princess .
He had to arrive at exactly 17h00.

If he travelled  at 15 km per hour, he would arrive one hour too early.
If he travelled at 10 km per hour, he would arrive one hour too late.

Questions :  1- At what time did he leave?
                        2- What distance did he travel?
                        3- At what speed did he travel?

See answer