Four people must cross a bridge at night with one torch.
Walking speeds: 1, 2, 5, 10 minutes.
Only two can cross at a time. The torch must come back each trip.
Fastest time everyone’s across?

Q: Four people must cross a bridge at night with one torch. Walking speeds: 1, 2, 5, 10 minutes. Only two can cross at a time. The torch must come back each trip. Fastest time everyone’s across?

17 minutes.. 1+2 over (2). 1 returns (1). 5+10 over together (10). 2 returns (2). 1+2 over again (2). That’s the slowest pair travelling together once — the secret most people miss.

Question

Accepted Answer

17 minutes. — 1+2 over (2). 1 returns (1). 5+10 over together (10). 2 returns (2). 1+2 over again (2). That’s the slowest pair travelling together once — the secret most people miss.