Thrilling Peril! - Futility Closet

Amy, Bob, Cindy, and Dave are the last four colonists on Mars, which is being overrun by Hideous Sand Beetles. The last evacuation ship leaves in 16 minutes. To reach it, they must pass through the Soul-Freezing Tunnel of Yx, which can accommodate only two people at a time. And anyone passing through the tunnel must light his way with the Fabulous Oracle of Zeb. (Mars is very dramatic.)

Amy can travel the tunnel in 1 minute.
Bob can travel the tunnel in 2 minutes.
Cindy can travel the tunnel in 5 minutes.
Dave can travel the tunnel in 8 minutes.

This is a problem. If Amy and Dave go first, they’ll reach the other side in 8 minutes (Dave’s top speed). If Amy then runs back and escorts Cindy, and then Bob, she and Bob will be only halfway through the tunnel when the ship departs. Are they doomed?

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No, they’re not doomed: Amy and Bob go first. (2 minutes) Bob returns with the oracle. (2 minutes) Cindy and Dave go together. (8 minutes) Amy returns with the oracle. (1 minute) Amy and Bob go last. (2 minutes) They reach the ship in 15 minutes.