: Bridge Riddle : the set-up

: Four young people are walking through the forest at night. Among them, they
: have one lantern to light their way. It's a thick forest, and the trail they're on
: isn't very well tread. The four companions follow the trail to an old wooden bridge
: over a large chasm. There's no way to get across the chasm without crossing the
: bridge.

: The bridge itself isn't in the greatest of shape, either. The four figure that it can
: only hold two of them at once, and no more. What's more, the bridge is missing
: some boards, so the two who are crossing will have to have the lantern. They can't
: all cross at the same rate though. The first person (we'll call him Adam) can cross
: the bridge in one minute. Chivon can cross it in two. Julio can cross in five minutes,
: and Jenn can cross in ten.

: Finally, it's getting really late, and the four young people don't want to be out in
: the middle of the forest much longer. What's the shortest amount of time they
: can cross the bridge?

: Hint and Clarifications:
: Get out a sheet of paper and write stuff out before you give up or look at the answer.
: If two people are crossing together, they travel at the slower person's time.
: No throwing the lantern across the chasm - you might lose it.
: No funny tactics either - the only way across the chasm is the bridge.
: The fastest time is a prime number.

: Good luck!

: To the answer