Similar Triangles
Triangles DEC and ABC have three pairs of angles equal in measure. If angle DEC is greater than angle EDC, then write as many possible proportions comparing the side lengths of the two triangles.

Extensions 
What if you start out with a triangle that has three pairs of equal proportions among the side lengths. What can you conclude about the angle measures?

Related External Resources 
Learning ratios and proportions through scale drawings
Teaching activity to gain an understanding of ratios and proportions through the use of scale drawings.
Oranges project
Students investigate the proportional relationship between the edible part of an orange and the peel or inedible part of a orange.
Ratio and proportion
A lesson plan in which the students will use the phenomenological approach to complete the activities, calculate ratios and proportions and compare and contrast group data with class data.
Similarity
A lesson plan in which the students will discover the factor of proportionality in similar polygons and to relate this factor to the perimeters and areas of similar polygons.
Submit your idea for an investigation to InterMath.
