Zombie escape.

problem

Thera are 4 people.
The 4 people are the Lab assistant, You, old professor and the janitor.
Zombie will catch up everybody in 17 minutes.
Everybody must get away from the zombies across the long bridge.
You take 1 minute.
The Lab assitant takes 2 minutes.
The old profeser takes 10 minutes.
The janitor takes 5 minutes.
The problem is how everybody can go across the bridge.

condition

They can be two by two at the same time on the bridge.
They need 1 lamp so when they finish acrossing the bridge,they need go back again.

solve

1. The two fastest ones across the bridge. It takes two minutes.
2. You come back. In total 3 minutes.
3. The old professor and the janitor across the bridge. There are 4 minutes left.
4. The lab assitant go back to you. In total there is 15 minute to take.
5. The lab assistant and you across to the bridge.
6. The final step, you will cut a bridge with a scissors to drop the zombies.

Good-bye everybody!!!!!