standard_description: Determine the unknown whole number in an addition or subtraction equation relating to three whole numbers. For example, determine the unknown number that makes the equation true in each of the equations 8 + ? = 11, 5 = �� – 3, 6 + 6 = ��.
problem_activity: Stage 1: Choose Your Unit
Required Preparation
Materials to Gather
Base-ten blocks
Connecting cubes
Paper clips (2-inch)
Materials to Copy
Blackline Masters
Estimate and Measure Stage 1 Recording Sheet

Narrative
Students choose an object and a familiar unit to measure it with. They estimate the length of the object and then measure to see the actual length to the nearest whole unit.
Variation:
Students may use base-ten cubes and add the length of two objects to practice adding within 100.
Additional Information
Gather or identify objects of various lengths that are less than 20 units (pencils, markers, books, glue, scissors, shoe, tape dispenser, side of desk).


aligns: no