In grade 1, students added and subtracted multiples of 10 within 100. In a previous unit, students represented three-digit numbers with base-ten blocks, drawings, and words. Students used equations to represent three-digit numbers as sums of the values of hundreds, tens, and ones, using the number and the name of each unit (235 = 2 hundreds + 3 tens + 5 ones) and expanded form ().

In this lesson, students add and subtract three-digit numbers and multiples of 10 and 100, using what they know about tens and hundreds. Students compare representations, such as base-ten blocks, base-ten diagrams, and equations, to understand that when adding or subtracting multiples of 10, the tens place changes, and when adding or subtracting multiples of 100, the hundreds place changes (MP7, MP8).