#### Material

1 large gray equilateral triangle.

2 green right-angled scalene triangles with black lines on the longer of the two sides enclosing the right angle; each green triangle is equal to one-half of the large gray triangle.

3 yellow obtuse-angled isosceles triangles; black lines on each of the sides enclosing the obtuse angle; each yellow triangle is equal to one-third of the large gray triangle.

4 red equilateral triangles; three have the black lines on one of the sides and one has a black line drawn on all three sides, each red triangle is one-fourth the size of the large gray triangle.

#### Presentation

- Invite the child to the lesson.
- Take out the large gray equilateral triangle.
- Place the green triangles together by the black lines.
- Place the gray triangle on top of the green triangles to show they are same size.
- Take off the gray triangle.
- Slide the green triangles to the top of the rug.
- Repeat this process for the 3 yellow triangles.
- Repeat this process for 4 red triangles.
- Randomize the triangles.
- Ask the child to explore.
- Tell the child to get you when he is done so that you can show him how to put the triangles back in the box in a good way.

#### Exercises

Child works independently.

#### Langauge

None, however when the child is around 5 or 6 years old, you can talk about the height, bisector, midpoint, and base of the triangles.

#### Control of Error

The black lines on each triangle; the gray triangle also acts as a control of error.

#### Direct Purpose

To show that an equilateral triangle can be divided into different kinds of triangles.

#### Indirect Purpose

Preparation for geometry.

Show that straight line figures are made up of triangles.

Preparation for understanding equivalence.

#### Age

4 to 4 1/2

#### Notes

A ribbon should be glued or taped to the bottom of the box to make removal of triangles easier.