Four men are crossing a bridge by night. One can cross in 1 minute, Two in 2 minutes, Three in 5 minutes, and Four in 10 minutes. To cross, they must carry a lantern, and a maximum two may cross simultaneously (when two people cross, it takes the longer of the two times to cross). Can they all cross in 17 minutes?
Assuming someone has to come back with the lantern...
1 and 2 cross in 2 minutes
1 comes back, 2+1=3
3 and 4 cross in 10 minutes, 3+10=13
Here's the trick, remember 2 is still on the destination side so he can quickly carry the lantern back to 1: 2 comes back, 13+2=15
1 and 2 cross in 2 minutes, 15+2=17
Assuming someone has to come back with the lantern...
1 and 2 cross in 2 minutes
1 comes back, 2+1=3
3 and 4 cross in 10 minutes, 3+10=13
Here's the trick, remember 2 is still on the destination side so he can quickly carry the lantern back to 1: 2 comes back, 13+2=15
1 and 2 cross in 2 minutes, 15+2=17
