: 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!