Chapter 9: Addition and Subtraction

Topic 9.1: Multi-Digit Addition with Regrouping (Carrying) and Estimation

Add 3- and 4-digit numbers with column alignment and regrouping, and check reasonableness using rounding estimation.

Topic 9.2: Multi-Digit Subtraction with Regrouping (Borrowing) and Word Problems

Subtract 3- and 4-digit numbers with borrowing across zeroes, and verify results using inverse addition.