I do have a question about # 13. I gat to 65 minutes minimum. The 5 minute walker takes the torch back 2x:
25 + 5, 20 + 5, & 10 = 65 minutes. I don't see how it is possible to get them all across the bridge in 60 minutes?
There is a quicker way though: let the 5 and 10 min walk first, then the 5min guy goes back (15 min passed), now the 20 and 25 min walk (40min passed) and the 10min guy goes back (50min passed), finally the 5 and 10min guy walk. So we get to the other side in 60min.