standard_description: Given a two-digit number, mentally find 10 more or 10 less than the number, without having to count; explain the reasoning used.
problem_activity: Stage 5: Subtract Two-digit Numbers
Required Preparation
Materials to Gather
Base-ten blocks
Number cubes
Materials to Copy
Blackline Masters
Target Numbers Stage 5 Recording Sheet

Narrative
Students subtract two-digit numbers to get as close to 0 as possible. Students start their first equation with 100. Then, they take turns rolling the three cubes to get a number to subtract. They choose one of the numbers on the cubes to represent the tens and the other number to represent the ones. Students subtract their tens and ones from the starting number. The difference becomes the first number in the next equation. The player who gets closest to 0 in 6 rounds, without going below 0, is the winner.
Additional Information
Each group of 2 needs 3 number cubes.


aligns: no