Back to School: A Contest

All day I've been thinking about today's post, and nothing's been coming to me — or rather too much has been coming to me, none of it appealing. Knitting, meh. Spinning, eh. Plastic flags, feh.

Which means it's time to fall back on plagiarism, er, I mean judicious borrowing, again. Miss B's math teacher is easing the class into the regular routine, which means over the weekend she had "fun" homework, specifically the following puzzle. Send your answer to rhymes with fuchsia [aht] cahmcahst [daht] net. There could be yarn riding on this; I'll decide what tomorrow, which will give me two posts for the price of one.

Al, Bob, Carl and Dave are all on the same side of a bridge they need to cross, but it's dark out and they have only one flashlight between them. The bridge can hold at most two people at a time, and whoever is crossing the bridge must have the flashlight with them. Each man walks at a different speed, so that each takes a different amount of time to cross the bridge:
A - 1 minute
B - 2 minutes
C - 5 minutes
D - 10 minutes
If two men cross together, they must walk at the slower man's speed.

They have 17 minutes to get all four of them across. How do they do it?

Note 1: this is a perfectly straightforward puzzle with no tricks. The flashlight can't shine a long way and can't be thrown. The men can't carry each other. The puzzle requires no math skills except logic and simple addition, which would explain why I was able to solve it.

Note 2: anyone who sends me an answer will be entered in the contest, even if their solution takes more than 17 minutes. The winner will be drawn at random. However, the first person to send me a correct answer will get a little something also.