Thinking Problem: Area of Triangles

1
A shaded rectangle has area of 140 cm2. In there,
the triangles are unshaded. Triangle ACB has the
area of 20 cm2. What fraction of the rectangle is
shaded?
20 cm2
140 cm2
70 cm2
2
A shaded rectangle has area of 140 cm2. In there,
the triangles are unshaded. Triangle ACB has the
area of 20 cm2. What fraction of the rectangle is
shaded?
20 cm2
20 cm2
140 cm2
70 cm2
50 cm2
The triangles area ½ of the rectangle
3
A shaded rectangle has area of 140 cm2. In there,
the triangles are unshaded. Triangle ACB has the
area of 20 cm2. What fraction of the rectangle is
shaded?
Shaded
50 cm2  140 cm2
20 cm2
20 cm2
140 cm2
70 cm2
50 cm2
Rectangle 140 cm2
Unshaded 90 cm2
4
This problem reinforces the area of
triangles in terms of rectangles.
Teaches to ignore excess information.
Reiterates concepts behind fractions.