Jon's MENSA Question of the Day

Thanks to my friend's MENSA Question of the Day book I have decided to add a little fun to the blog. Feel free to submit your answers in the comments section. The answer for today's question will be given next week in a seperate posting.

I know...Google is out there to help, but do not do that. This is to test your knowledge, not your answer hunting skills. It is on your honor, but please use honor.

Without further ado, here is today's question:

Our hero the brave knight, is trying to rescue the beautiful Princess of Puzzleland. The maiden has slipped him a message. She will be able to stand at the stable gate from 12:30 to 12:40--but no more than those ten minutes--on the following day. If he arrives promptly, she will elope with him. If not, she will be married later that same evening to his hated rival. The castle is 12 miles away. The first third is uphill, and his horse can make 4 miles per hour uphill; the second third is level, at 8 miles per hour, and the last part, one-third, is downhill, at 12 miles per hour. He figures that that averages out to 8 miles per hour, so if he leaves at 10:55 to give himself five minutes leeway, he should arrive exactly within the 10 minutes. Of course, he can't get there too early, or he'll be caught hanging around. Does he make it in time? Why or why not?