standard_description: Derive the formula A = 1/2 ab sin(C) for the area of a triangle by drawing an auxiliary line from a vertex perpendicular to the opposite side.
problem_activity: Stage 5: Cover (up to 20)
Required Preparation
Materials to Gather
Cups
Two-color counters
Materials to Copy
Blackline Masters
Shake and Spill Stage 4 and 5 Recording Sheet (G1 and 2)

Narrative
Students decide together how many counters, between 11–20, to use. Partner A closes their eyes while Partner B shakes, spills, and covers up the yellow counters with a cup. Partner A determines how many counters are under the cup and explains how they know. Both partners record the round. Switch roles and repeat.
Additional Information
Each group of 2 needs a cup and 20 two-color counters.


aligns: no