Subtracting Multiples of Ten

Active learning works for this topic because subtracting multiples of ten relies on students visualizing how only the tens digit changes while the ones digit stays the same. Concrete materials and collaboration help students internalize this abstract idea by making the invisible remain visible.

• 1st Grade
• Mathematics
• 4 activities
• 15 min–25 min

Learning Objectives

1. Calculate the difference between two multiples of ten within 100.
2. Identify the digit that changes when subtracting a multiple of ten from a two-digit number.
3. Explain why the ones digit remains constant when subtracting multiples of ten.
4. Compare the results of subtracting different multiples of ten from the same two-digit number.

Think-Pair-Share

⏱ 15 min·Pairs

Think-Pair-Share: What's Left in the Ones?

Present 63 - 40. Partners individually predict the result and specifically predict what the ones digit will be before solving. They share predictions, then use a hundreds chart or base-ten blocks to verify. The class discusses why every pair got the same ones digit even when their solving strategies differed.

Prepare & details

Explain how subtracting a multiple of ten only affects the tens digit.

Facilitation Tip: During Think-Pair-Share, circulate and listen for students who notice the ones digit stays the same, then invite them to share their observation with the class.

Setup: Standard classroom seating; students turn to a neighbor

Materials: Discussion prompt (projected or printed), Optional: recording sheet for pairs

• Understand
• Apply
• Analyze
• Self-Awareness
• Relationship Skills

Inquiry Circle

⏱ 20 min·Small Groups

Inquiry Circle: Rod Removal

Groups build a two-digit number with rods and unit cubes. One student removes a specified number of rods (e.g., 3 rods for subtracting 30) while another watches the units and confirms they never change. The group records the before and after numbers and writes the equation.

Prepare & details

Predict the result of subtracting 10 or 20 from a given two-digit number.

Facilitation Tip: In Rod Removal, remind students to verbalize what they see happening to the rods and unit cubes as they physically remove them.

Setup: Groups at tables with access to source materials

Materials: Source material collection, Inquiry cycle worksheet, Question generation protocol, Findings presentation template

• Analyze
• Evaluate
• Create
• Self-Management
• Self-Awareness

Gallery Walk

⏱ 20 min·Pairs

Gallery Walk: Hundreds Chart Trails

Post hundreds charts with a start number circled. Students visit each chart, draw arrows moving up the specified number of rows to subtract a given multiple of ten, and write the equation. Pairs compare charts and discuss why moving up on the hundreds chart subtracts tens.

Prepare & details

Design a mental strategy for subtracting multiples of ten.

Facilitation Tip: For Hundreds Chart Trails, ask students to point to each number they land on and explain why the ones digit didn't change.

Setup: Wall space or tables arranged around room perimeter

Materials: Large paper/poster boards, Markers, Sticky notes for feedback

• Understand
• Apply
• Analyze
• Create
• Relationship Skills
• Social Awareness

Stations Rotation

⏱ 25 min·Small Groups

Stations Rotation: Mental Subtraction Ladders

At each station a ladder shows a starting two-digit number. Students subtract a given multiple of ten at each rung and write the result, varying the multiple (10, 20, 30) and starting number across stations. Students explain their mental strategy aloud to a partner before writing the answer.

Prepare & details

Explain how subtracting a multiple of ten only affects the tens digit.

Facilitation Tip: At Mental Subtraction Ladders, challenge students to explain their jumps aloud before writing the answer to reinforce place-value reasoning.

Setup: Tables/desks arranged in 4-6 distinct stations around room

Materials: Station instruction cards, Different materials per station, Rotation timer

• Remember
• Understand
• Apply
• Analyze
• Self-Management
• Relationship Skills

Teaching This Topic

Teachers should emphasize place value by modeling subtraction with base-ten blocks first, then transitioning to mental math. Avoid teaching subtraction as a digit-by-digit process, which can reinforce misconceptions. Research suggests that students benefit from repeated exposure to visual models before abstract symbols, so rotate materials until the concept clicks.

What to Expect

Successful learning looks like students confidently subtracting multiples of ten while explaining that the ones digit remains unchanged. They should use place-value language to describe their process and correct peers when they notice the ones digit shifting.

Watch Out for These Misconceptions

Common Misconception

During Collaborative Investigation: Rod Removal, watch for students who remove both rods and unit cubes when subtracting a multiple of ten.

What to Teach Instead

Have students physically remove only the rods while keeping the unit cubes in place, then ask them to count the remaining blocks to see the ones digit stayed the same.

Common Misconception

During Think-Pair-Share: What's Left in the Ones?, watch for students who think the ones digit cannot stay the same if the tens digit is too small.

What to Teach Instead

Use rods to show that removing 2 rods from 2 rods leaves 0 tens, while the 3 unit cubes remain untouched, proving the ones digit doesn’t depend on the tens digit.

Assessment Ideas

Exit Ticket

After Station Rotation: Mental Subtraction Ladders, give students a card with a problem like '60 - 30 = ?' and '75 - 20 = ?'. Ask them to write the answer and circle the digit that changed in the second problem. Then, ask them to write one sentence explaining why the other digit did not change.

Quick Check

During Gallery Walk: Hundreds Chart Trails, display a number on the board, such as 48. Ask students to hold up fingers to show how many tens they would subtract (e.g., 1, 2, or 3). Then, ask them to write the resulting number on a mini-whiteboard and hold it up. Discuss the ones digit for each result.

Discussion Prompt

After Collaborative Investigation: Rod Removal, pose the question: 'Imagine you have 50 blocks. You take away 20 blocks. How many are left? Now, imagine you have 58 blocks and you take away 20 blocks. How many are left? What is the same about these two problems?' Facilitate a discussion about the role of the ones digit.

Extensions & Scaffolding

• Challenge students who finish early to create their own subtraction problems using multiples of ten and trade with a partner for solving.
• Scaffolding for struggling students: Provide base-ten block mats and have them subtract rods while you ask, 'What happened to the unit cubes?'
• Deeper exploration: Ask students to write a word problem involving subtracting a multiple of ten from a two-digit number and solve it with a model.

Key Vocabulary

Multiple of Ten	A number that can be divided by 10 with no remainder. Examples include 10, 20, 30, up to 100.
Tens Digit	The digit in a two-digit number that represents the number of tens. For example, in the number 53, the tens digit is 5.
Ones Digit	The digit in a two-digit number that represents the number of ones. For example, in the number 53, the ones digit is 3.
Place Value	The value of a digit based on its position within a number. This helps us understand that the tens digit represents groups of ten and the ones digit represents individual units.