The purpose of this activity is for students to subtract numbers within 1,000, using any strategy that makes sense to them to find the difference of two numbers within 1,000. The expressions in this activity give students a chance to use different strategies, such as subtracting hundreds from hundreds, tens from tens, and ones from ones, or adding up. Students also may use a variety of representations, which will be the focus of the Activity Synthesis. Students who choose to use base-ten blocks or number lines to represent their thinking use tools strategically (MP5).

This activity uses MLR7 Compare and Connect. Advances: representing, conversing.

Representation: Develop Language and Symbols. Synthesis: Invite students to explain their thinking orally instead of through a display.
Supports accessibility for: Social-Emotional Functioning and Fine Motor Skills.

MLR7 Compare and Connect

• “Create a display that shows how you found the value of ______. You may want to include details, such as notes, diagrams, drawings, and so on, to help others understand your thinking.”
• 2–5 minutes: partner work time
• 5–7 minutes: Gallery Walk
• “What is the same and what is different about the ways that the groups represented the subtraction?” (Some groups used equations. Some groups used base-ten blocks. All used the same numbers. All got the same answer.)
• Display one example of 2 or 3 different representations side by side.
• “Which representations show the same idea or help us find the difference the same way?” (The number line and equations show the same idea of adding up. The base-ten blocks are different because they show a ten or a hundred decomposed into smaller units before some of the blocks are taken away.)

The purpose of this activity is for students to make sense of drawings of base-ten blocks. Students compare two base-ten drawings. The first drawing is the same as what they saw in grade 2, in which the tens block is decomposed into 10 individual ones and moved over to the ones place before subtracting the ones. In the second drawing, the tens block is moved over and partitioned into 10 parts but not decomposed into individual ones. The subtraction of ones is shown directly on the ten that was moved over. Students then match base-ten diagrams to subtraction expressions and subtract to find the value of each expression. This will be helpful in later lessons when students relate base-ten diagrams to written algorithms.

• Invite students to share the expression that matches each diagram.
• “What did you have to notice as you matched each diagram to an expression?” (I had to look at the numbers to see where I needed to decompose a hundred or a ten. I saw that the first diagram shows ones left over, with decomposing a ten. The second diagram shows no ones left over, without decomposing. The third diagram shows a one left over, with decomposing a hundred.)