## Lesson: Adding and Subtracting Two-Digit Numbers and Money Amounts

Developing the Concept

Begin by reviewing basic one-digit subtraction facts. When children demonstrate proficiency with these facts, explain that they will next learn how to subtract two-digit numbers.

**Materials:** blank transparency, overhed base-ten blocks, coins

**Preparation:** Draw a tens-and-ones frame on the transparency. Have children practice using a tens-and-ones frame and base-ten blocks to represent two-digit numbers.

**Prerequisite Skills and Concepts:** Children should have a solid grasp of subtraction of basic facts.

**Wrap-Up and Assessment Hints**

Give children addition and subtraction exercises that include adding or subtracting multiples of ten and adding or subtracting one-digit numbers. Suggest that they choose any method they wish to solve them—paper and pencil, base-ten blocks, or basic facts. You can assess children's progress informally by asking them to explain why they chose their method.