Why do so many puzzles involve crossing rivers?

Seriously, there’s the one with the cabbage, goat and wolf (and variations thereof), there’s the Bridges of Konigsberg, and this one. When it comes to weirdly common puzzle scenarios, it’s right up there with drawing paired socks at random and turning two triangles into four. Puzzlers might have too much free time on their hands. *laughs*

ANYWAY. I digress.

A buddy of mine sent me a brain teaser the other day, and it seemed like the perfect challenge for my fellow puzzle fans. Although it tends a bit more toward the mathematical-word-problem side than a straight brain teaser, I think it will get your deductive juices flowing!

Bridge and Torch

Four people come to a narrow bridge at night. Among them, they have one torch, which has to be carried in order for anyone to cross.

Only two people can cross the bridge at a time. Person A can cross the bridge in 1 minute, B in 2 minutes, C in 5 minutes, and D in 8 minutes. When two people cross the bridge together, they go at the slower person’s pace.

How can they all cross the bridge in 15 minutes or less?

(Oh, before I go… a quick bit of internet sleuthing reveals that this puzzle originated in Garth Sundem’s Brain Candy: Science, Paradoxes, Puzzles, Logic, and Illogic to Nourish Your Neurons. Credit where credit is due, always. Enjoy!)