Camping Logic

[AB Editor]

Four people need to cross a rickety rope bridge to get back to their camp at night.

Unfortunately, they only have one flashlight and it only has enough light left for seventeen minutes.

The bridge is too dangerous to cross without a flashlight, and it's only strong enough to support two people at any given time.

Each of the campers walks at a different speed. One can cross the bridge in 1 minute, another in 2 minutes, the third in 5 minutes, and the slow poke takes 10 minutes to cross.

How do the campers make it across in 17 minutes?

[dr b]

assuming one is allowed to walk slower than their "fast speed" if needed:

1&2 cross, 1 returns (3 minutes gone)
5&10 go across, 2 returns (12 minutes; 15 minutes in total gone)
1&2 cross (2 minutes, 17 in total)

[wildwood]

1 and 2 cross together = 2 minutes.
2 goes back = 4 minutes
5 and 10 cross = 14 minutes
1 goes back. The torch has now been used 15 minutes.
Finally 1 & 2 goes across = 17 minutes.