Two problems for YOU to solve

I'd like for you to try solve these two 5th grade problems. They are from a very nice collection of word problems for kids by Canada's SchoolNet.

I'd like to use them to illustrate problem solving. But before I do that and give you the solutions, please try to solve them yourself. And don't post solutions here for now; I will have to reject such comments.

Solutions and discussion will follow in a few days.

THE FIRST PROBLEM IS:

* How many addition signs should be put between digits of the number 987654321 and where should we put them to get a total of 99?

THE SECOND IS:

* Divide the face of the clock into three parts with two lines so that the sum of the numbers in the three parts are equal.

Comments

mathmom said…
Those are nice problems. I think most 5th graders would have trouble with them. They'd be tough with plain guess-and-check, which is what I think most 5th graders would try. I'll see what my 6th grader can do with them.

Your link to the source of the problems is broken by the way.
8:05 PM, January 13, 2008
mathmom said…
My 6th grade son did solve these, and he did use similar methods to those I used (since I teach math problem solving at his school, I guess that is hardly shocking). He came up with a different answer than I did to the first one, but it is also correct. Now that I look more closely, I would claim that he and I have the only two possible different solutions to that problem.

I'm looking forward to the discussion of these problems.
8:25 PM, January 13, 2008
Anonymous said…
Here's a related problem (to #1): Quick Sum Puzzle.

We can quickly verify that there are only two solutions, one slightly more economical than the other.

The second problem is tricky enough just looking for a solution, but gets harder trying to demonstrate that the solution is unique.
11:46 PM, January 14, 2008
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