My area and perimeter unit is seriously one of my favorite things to teach in fifth! I love the formulas, the real life math experiences, and the hands on learning that can happen. This week, I did a simple, yet totally powerful demonstration to help my students discover, and most of all remember, the formula for the area of a triangle.
I gave each student a 5 inch by 5 inch square. We used our rulers to measure five rows and five columns to show the area of our square.
Last year, I used a 4 inch by 4 inch square. I am seriously struggling with which was the better alternative for this activity. A 5×5 square will yield an area of a triangle with a decimal. Since my kids were fairly comfortable with this, I went with it! 🙂
This is 100% review for my fifth graders, but that was also 100% the point! I wanted my kids to see that finding the area of a triangle can be SUPER intimidating, but it is actually very similar to something that they are already experts at doing!
I had them lay their gridded square on their notebook. Then, we wrote the formula area = length x width, and calculated the area.
Then, I said, “But hey….aren’t we talking about the area of a TRIANGLES today?! Errrr, that’s embarrassing. Can we somehow make this square into a triangle?” <—–Unfortunately, I do say silly, sarcastic things like this!
They quickly discovered that by folding it in half, they could easily make a triangle.
They counted the squares and were able to calculate the area of the triangle without the use of a formula.
Then, I told them that I wanted to leave them alone for a while, and give them a chance to brainstorm a possible formula. The lightbulbs were seriously going off like crazy!
After working through a few examples, and testing their possible formulas, we practiced finding the area of triangles with a game of Scoot!