Four people want to cross a bridge. They all begin on the same side. It’s night time and they only have one flash light with them. At most two people can cross the bridge at the same time, and any party who crosses, either one or two people must have a flashlight with them. The flashlight must be walked back and forth not thrown etc. Each person walks at a different speed. A pair must walk together at the pace of the slower person.

Question

One person needs one minute to cross, another needs 2 minutes to cross, another needs 5 minutes and another needs 10 minutes. How can all the people get across the bridge in 17 minutes?

Answer 1

call those person a,b,c, d
a and b go across: 2 minutes
b returns with flash: 2 minutes
c and d go across: 10 minutes
a returns with flash: 1min
a and b go across: 2 min