This Add and Subtract Using Place Value lesson plan also includes:
Given a number between 10 and 99, learners use place value and properties of operations to add and subtract 10. The goal is to have them mentally calculate the number, and to refrain from counting or using manipulatives. Learners explain their processing orally, and could even draw an image showing what they are doing in their mind. Extension activities are available, and include using higher numbers.