100th Day Thinking

We always celebrate the 100th day of school.  Sadly, I really did not enjoy the activities we have used. They just seemed too easy. I began searching for a math investigation activity.  I found this site in my quest.  Debbie of Debbie’s Dabblings gave me permission to share her site and 100th day post. Please click below to read more about her amazing classroom.


Here is the link to the 100th Day post.


Even though I teach 2nd graders, I felt they could successfully complete the booklet with a little guidance.  They did very well. I was proud BUT I was floored when we tried this one section of the booklet.

Here’s the question:

 How many centimeters tall would a stack of 100 pennies be?

So I have to admit that when we started this exploration, I thought I might need to swoop in and help a lot. When I posed the first question, the first words out of their mouths were “The stack will fall over!”  I reminded them that most problems can be solved if they just make it a simpler problem. One student said, “We could make 10 stacks of 10 and measure one to solve it.” They marched off happily in small groups to try it out.

Once they found out that 10 pennies equals 1 1/2 centimeters, the real thinking began because they had to solve for all 100 pennies. Second graders normally learn to recognize fractions and sets but rarely do they do a lot of work beyond that objective.

Below are 2 videos of different ways they figured out how many centimeters tall 100 pennies would be.  They speak very softly and others are still talking and working in various stages in the background. You will have to turn your volume all the way up. 🙂

Explanation 1

In case you could not hear: They knew all 10 stacks would have 10 centimeters all together. Then they added the halves. They knew 2 halves made 1 and they had 5 of those sets  so 10 + 5 = 15.

Explanation 2

In case you could not hear it: They put 2 stacks together since that made 3 centimeters. Then they counted by 3’s to make 15.

I was a happy (even happier than normal, which is saying a lot) teacher that day but even better, they were proud and excited about their thinking.