Question 96918: This problem is word for word from a homework assignment where the kids are allowed to get help.
Four people are on a team in a race. It is night time and the team comes to an old rickety bridege. The bridge looks pretty frail and the team thinks that at most only ttwo people can be on the bridge at one time. The team has one flashlight among them. The bridge has gaps in it and whoever crosses the bridge must have the flashlight. That is to say the flashlight must cross the bridge every time. It takes each person a different time to cross the bridge. It takes person A 10 minutes to cross the bridge by themselves, B 5 minutes, C 2 minutes and D 1 minute.
The rules are as follows:
1) If two people cross the bridge the time it takes is as slow as the slowest person crossing at the time.
2) The flashlight cannot leave the team's hands (it can't be thrown, tossed, rolled, etc--it must cross with someone)
3) No carrying of people, so no piggyback riding.
Question: What is the SHORTEST time it takes all four people to get across? (Don't forget to add time for return trips also).
Ex. A & D go together-10 min.
A comes back-10 minutes.
A & C go together- 10 min.
A comes back-10 min.
A & B go together-10 min.
All people are across and it took 50 minutes.
(This is not the correct answer, just an example of how the problem should be done)
Answer by scott8148(6628)   (Show Source):
You can put this solution on YOUR website! you want the fastest person (D) to do the most crossing
D accompanies each person across and returns for the next person
3 crossings (10+5+2) and 2 returns (1+1) for a total of 19 minutes
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