Answer to April 21, 2003 Problem

The Boat Problem

A family of four and their cat get trapped on an island when rising flood waters tear out the bridge they used just a few hours before. Frantically they search for some means of crossing back to the mainland and finally, when they've just about given up hope, the son says, "I found a small boat and oars." They gather around but their joy is short lived because the manufacturer's instructions printed on the back of the boat says the boat can carry only 180 pounds. Thank goodness Mr. Pleacher's not here. It's just Mom, Dad, the two kids and the cat. And none of them can swim.

So the boat can carry only 180 pounds. Well, the father weighs 170. The mother says she weighs 130. The son is 90 pounds. And the daughter is 80. The cat weighs 15 pounds. Everyone can row except the cat.

What is the fewest number of crossings to save everyone?
Explain how to make the crossings.

 

Solution to Problem:

The fewest number of crossings is nine.

The boy and the girl row over to the mainland.
And that's 170 pounds.

One of them comes back. Doesn't matter which one.
The next trip the mother and the cat row to safety. So now we got one of the kids over there, the mother and the cat.

Now the other kid comes back. So the only two that have reached safety so far are the mother and the cat.

The boy and the girl row over again. One of them comes back.

The father rows over. The other kid comes back to the island and now the two kids row to safety together.


Correctly solved by:

1. Matt Stillwagon Winchester, Virginia
2. Jeffrey Gaither Winchester, Virginia
3. James Alarie University of Michigan -- Flint
Flint, Michigan
4. Rick Jones Kennett Square, Pennsylvania
5. John Funk Ventura, California
6. William Funk San Antonio, Texas
7. George Gaither Winchester, Virginia
8. Walt Arrison Philadelphia, Pennsylvania
9. Johan Bernström Tullängskolan, Örebro, Sweden
10. Misty Carlisle Winchester, Virginia
11. Michael Rodiguez Great Falls, Montana