There are four people who need to cross a bridge at night. The
bridge is only wide enough for two people to cross at once. There is
only one flashlight for the entire group. When two people cross,
they must cross at the slower member's speed. All four people must
cross the bridge in 17 minutes, since the bridge will collapse in
exactly that amount of time. Here are the times each member takes to
cross the bridge:
Person A: 1 minute
Person B: 2 minutes
Person C: 5 minutes
Person D: 10 minutes
If Person A and C crossed the
bridge initially, 5 minutes would elapse, because Person C takes 5
minutes to cross. Then Person A would have to come back to the other
side of the bridge, taking another minute, or six minutes total.
Now, if Person A and D crossed the bridge next, it would take them
10 minutes, totaling to 16 minutes. If A came back, it would take
yet another minute, totally 17. The bridge would collapse with A and
B on the wrong side. How can all four people get across the bridge
within 17 minutes? Note: there is no trickanswer to this problem.
You cannot do tricky stuff like throwing the flashlight etc.
1.
A and B cross together. Total Time: 2 Minutes
2.
B comes back. Total Time: 4 Minutes
3.
C and D cross together. Total Time: 14 Minutes
4.
A comes back. Total Time: 15 Minutes
5.
A and B cross together. Total Time: 17 Minutes
