A family of four and their dog are trapped on an island, when rising floodwaters tear out the bridge that they had used just a few hours earlier. When they had just given up hope the son says, “I’ve got a small boat and oars.”
But their joy was short-lived. The manufacturer’s instructions printed on the boat’s stern said that the boat can carry only 180 pounds.
The dog is the only one who can swim.
The father weighs 170. The mother says she weighs 130 but it’s more like 155. The son is 90 pounds, the daughter is 80, and the dog is 15.
Here’s the question: What’s the fewest number of crossings they have to make to save everybody?
May 3rd, 2011 | Category: 
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if they all grab on to the side of the boat. and kick with their feet. and use the boat as a floating devise. they could do it in One trip.
Or, do they also not know how to kick?
They do not know how to kick plus the waters are swarming with piranhas.
Keep trying.
It’s all about the kids and their rowing abilities. The two kids (90+80=170) row across and one gets out (say the girl). The son then rows back to the island (90) and the dieting mum crosses alone (155). The daughter then brings the boat back (80) and picks up the the boy and again they row across (170). This time the boy stays because he’s a mama’s boy and the girl returns to the island (80). The dad then crosses alone (170) and now that the son is rested he rows back to the island (90) to pick up his sister and for the last time they row across (170), while the dog (15) follows along swimmingly. That’s over to the main land, back to the island, over, back, over, back, over, back and over – so, nine trips.
Considering the dog probably wouldn’t survive the swim across the piranha infested river, he may have opted to jump in the boat with the mum totaling between 145 and 170 pounds on the third of nine river crossings.
Or Not
You’re correct, Paul!
The boy and the girl row over to the mainland. The girl rows back leaving the boy on the mainland. The next trip the mother and the dog row to safety. Next, the boy rows back leaving the mother and the dog safely on the mainland. This time, the boy and the girl row over again. The boy hops off the boat and the girl rows back to the island. Now the father rows over to the mainland alone. When he arrives, the boy comes back to the island and now the two kids row to safety together. That makes nine crossings.
You’re today’s winner.