Adding Multiples of Ten

Active learning works well for adding multiples of ten because students need to physically and visually see how the tens place changes while the ones stay the same. This hands-on approach builds a strong foundation in place value, making abstract ideas more concrete and easier to grasp.

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

Learning Objectives

1. Calculate the sum of a two-digit number and a multiple of ten (10, 20, 30) using base-ten blocks.
2. Explain how adding a multiple of ten to a two-digit number affects the tens digit and the ones digit.
3. Predict the result of adding 10, 20, or 30 to a given two-digit number without using manipulatives.
4. Design a personal strategy for mentally adding multiples of ten to two-digit numbers.
5. Compare the sums of different two-digit numbers when adding the same multiple of ten.

Inquiry Circle

⏱ 20 min·Pairs

Inquiry Circle: What Changed?

Partners build a two-digit number with base-ten blocks, then add one rod (ten) at a time. After each addition, they record the new number and circle what changed. Groups compile results and share their pattern discovery with the class.

Prepare & details

Explain how adding a multiple of ten only changes the tens digit.

Facilitation Tip: During Collaborative Investigation: What Changed?, circulate and ask guiding questions like 'What stayed the same in your rods and units?' to keep students focused on the key idea.

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

Think-Pair-Share

⏱ 15 min·Pairs

Think-Pair-Share: Predict the New Number

Announce a starting number (e.g., 34). Ask partners to predict what 34 + 20 will be before any calculation. Each partner shares their prediction and reasoning. The class tests predictions with a hundreds chart or base-ten blocks and discusses why the ones digit never moved.

Prepare & details

Predict the outcome when adding 10, 20, or 30 to a given number.

Facilitation Tip: For Think-Pair-Share: Predict the New Number, provide sentence stems like 'I think the new number will be ____ because ____' to structure student responses.

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

Gallery Walk

⏱ 20 min·Small Groups

Gallery Walk: Hundreds Chart Hop

Post large hundreds charts around the room with a starting number circled. Students rotate and draw an arrow showing the result of adding a given multiple of ten (10, 20, or 30). They record the equation and explain in one sentence why the ones digit stayed the same.

Prepare & details

Design a mental strategy for quickly adding multiples of ten.

Facilitation Tip: In Gallery Walk: Hundreds Chart Hop, place sticky notes with follow-up questions like 'How did moving down the chart affect your number?' near each station.

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 Math Challenge

Each station provides a starting number and a multiple of ten to add (presented with blocks, a hundreds chart, and numerals only). Students solve mentally at the numeral station and explain their strategy, building toward fluent mental addition of multiples of ten.

Prepare & details

Explain how adding a multiple of ten only changes the tens digit.

Facilitation Tip: During Station Rotation: Mental Math Challenge, listen for students using skip-counting or place value talk to solve problems, not counting by ones.

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

Teach this topic by first using manipulatives like base-ten rods and units so students see the physical change in the tens place while the ones remain unchanged. Model think-alouds to verbalize the process, then gradually move to mental math and abstract representations. Avoid rushing to written algorithms before students understand the place value shift. Research shows that students who visualize the hundreds chart or number line develop stronger mental math strategies for adding tens.

What to Expect

Successful learning looks like students confidently adding multiples of ten without counting by ones, explaining why only the tens digit changes, and using place value language to describe their process. They should also transfer this skill to real-world contexts like money or number lines.

Watch Out for These Misconceptions

Common Misconception

During Collaborative Investigation: What Changed?, watch for students who change both digits when adding tens.

What to Teach Instead

Have students use base-ten rods and units to physically add only rods while keeping the units in place, then ask them to describe what they observe about the ones digit.

Common Misconception

During Station Rotation: Mental Math Challenge, watch for students who count by ones to add a multiple of ten.

What to Teach Instead

Guide students to use the skip-count-by-tens sequence on the hundreds chart or number line to build a mental framework for efficient computation.

Assessment Ideas

Quick Check

After Collaborative Investigation: What Changed?, present students with a number line from 10 to 100. Ask them to mark where 45 would be, then circle 55, 65, and 75. Ask: 'What do you notice about the numbers you circled?'

Exit Ticket

After Station Rotation: Mental Math Challenge, give each student a card with a problem like '32 + 20 = ?'. After they solve it using drawings or mental math, ask them to write one sentence explaining how adding 20 changed the number 32.

Discussion Prompt

During Gallery Walk: Hundreds Chart Hop, pose the question: 'If you have 57 cents and you find 3 more dimes, how much money do you have now? Explain your thinking.' Encourage students to share different strategies they used to solve the problem during the wrap-up discussion.

Extensions & Scaffolding

• Challenge: Provide three-digit numbers and ask students to add multiples of ten, explaining how the tens and hundreds places change.
• Scaffolding: Give students a hundreds chart with only the tens row highlighted to support counting by tens.
• Deeper Exploration: Have students create their own word problems involving adding multiples of ten and swap with peers to solve.

Key Vocabulary

Multiple of Ten	A number that can be divided by 10 with no remainder, such as 10, 20, 30, 40, and so on.
Two-Digit Number	A whole number greater than or equal to 10 and less than or equal to 99, consisting of a tens digit and a ones digit.
Tens Digit	The digit in a two-digit number that represents the number of tens.
Ones Digit	The digit in a two-digit number that represents the number of ones.
Base-Ten Blocks	Manipulatives used to represent numbers, where rods represent tens and small cubes represent ones.