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 fourth takes 10 minutes to cross.

How do the campers cross the bridge in 17 minutes?

Answer

Let:

- Camper 1 = C1 (1)
- Camper 2 = C2 (2)
- Camper 3 = C3 (5)
- Camper 4 = C4 (10)

This is how they cross the bridge:

- C1,C2 → (2)
- ← C2 (2)
- C3,C4 → (10)
- ← C1 (1)
- C1,C2 → (2)

The time in brackets () indicate the time taken to cross the bridge. If you sum them up, it will add up to 17 minutes.