Lesson 12

Practice With Proportional Relationships

Lesson Narrative

This optional lesson gives students an additional opportunity to practice finding unknown values in proportional relationships using contextual examples. The problems preview using the Pythagorean Theorem, which is a key idea in a subsequent lesson. They also preview finding all unknown values in right triangles, which is a key idea in a subsequent unit. Students have a chance to reason abstractly and quantitatively as they think about whether their answers make sense in context (MP2).

Learning Goals

Teacher Facing

  • Calculate unknown values in proportional relationships.
  • Determine scale factors to describe similar figures (using words and other representations).

Student Facing

  • Let’s find unknown values in proportional relationships.

Learning Targets

Student Facing

  • I can find scale factors and use them to solve problems.

CCSS Standards


Glossary Entries

  • similar

    One figure is similar to another if there is a sequence of rigid motions and dilations that takes the first figure onto the second.

    Triangle \(A'B'C'\) is similar to triangle \(ABC\) because a rotation with center \(B\) followed by a dilation with center \(P\) takes \(ABC\) to \(A'B'C'\).

    Triangle ABC, rotated and then dilated.