Mme Christine, Mme Nona, Mme Lichimo and Mme Lapierre are out walking: They come to a rickety old wooden bridge. The bridge is weak and only able to carry the weight of two of them at a time. Because they are in a rush and the light is fading, they must cross in the minimum time possible and must carry a flashlight on each crossing.
They only have one flashlight and it can't be thrown. Because of their different fitness levels and some minor injuries, they can all cross at different speeds. Mme Christine can cross in 1 minute, Mme Nona in 2 minutes, Mme Lichimo in 5 minutes and Mme Lapierre in 10 minutes (she has an injury, her slowness is not due to fitness level!).
There is a Staff Meeting starting on the far side of the bridge in 17 minutes ... can they all make it? No tricks allowed ... they all must cross the bridge with a light (no more than 2 at a time), no throwing the flashlight, no piggy-backing, one does not start walking back with the flashlight while the other finishes crossing, etc.
Ready for the answer?