Subtraction of 2 Digit Numbers

Week 1

Learning Outcome

Subtracts two numbers up to 99 using place value and regrouping.

Objective

Children will be able to use base ten blocks to understand the concept of subtraction of two-digit numbers.

Prerequisites

  • Children can perform single-digit subtraction.
  • The teacher can have a simple check for understanding at the beginning of the lesson by showing flashcards and asking the children to solve single-digit subtraction problems.

Pre-teach Vocabulary

Children should be familiar with the terms such as, take away, less, before, and remaining.

Introduction

Materials required:

  • 9 objects available (pencils, fruits, etc.)
  • Basket (1)
  • A4 sheet
  • Single Blocks (9)
  • A Set of 10 blocks (9)

The teacher could begin by reviewing the topic of subtraction using a few objects. The teacher shows a basket containing 6 apples and asks the children how many apples will remain if we take away 4 apples.

  • Now the children will be able to count the remaining apples in the basket and say the answer is 2. The teacher writes the answer on the board. 6 – 4 = 2
  • The teacher will show other available objects and tell them to take away a few objects to find how many are left.
  • The teacher will encourage the children to respond with more examples.

Teaching Method: I Do – We Do – You Do

I Do (Teacher Modelling):

Today, we are going to learn how to subtract two-digit numbers using base ten blocks. Base ten blocks help us see the tens and ones clearly, so subtraction is easier to understand.

  1. Display the problem, 45 – 23, on the board.
  2. Show 4 tens blocks and 5 ones blocks to represent 45.
  3. First, I represent the number 45 using base ten blocks – 4 tens and 5 ones.
  4. Now I need to subtract 23 from 45. That means I take away 2 tens and 3 ones.
  5. Physically remove 2 tens blocks and 3 ones blocks.
  6. Count what’s left. 2 tens blocks and 2 ones blocks = 22.
  7. So, 45 minus 23 equals 22.
  8. Say Aloud:
    1. I always start by looking at the ones. If I have enough to subtract, I do it. If I don’t, I may need to regroup.
    2. Then I subtract the tens.
  9. Take 62-34 for instance
  10. Ask children: Let’s build 62 together. How many tens are there in the number 62? (Answer: 6). How many ones are there in the number 62? (Answer: 2).

Work together:

  • Build 62.
  • Now, we need to subtract 34. Can we take 4 ones from 2 ones?
  • No, so we need to regroup.
  • Exchange 1 ten for 10 ones. Now we have 5 tens and 12 ones.
  • Subtract 4 ones from 12 ones. We are left with 8 ones.
  • Subtract 3 tens from 5 tens. We are left with 2 tens.
  • What is the answer? 2 tens and 8 ones = 28.
  • So, 62 – 34 = 28

We Do (Guided practice):

Let’s solve 64 minus 32 using base ten blocks. What do we do first?

  • Ask: How many tens are there in 64? (Answer: 6 tens)
  • How many ones are there in 64? (Answer: 4 ones)
  • Build 64 using 6 tens blocks and 4 ones blocks.
  • Now we subtract 32. That is 3 tens and 2 ones.
  • Ask, ‘Do we have enough ones to subtract 2?’ (Yes!)
  • Remove 2 ones blocks. We are left with 2 ones blocks.
  • Remove 3 tens blocks. We are left with 3 tens blocks.

Conclusion:

  • What’s left? 3 tens blocks and 2 ones blocks.
  • So, 64 – 32 = 32.

Reinforce:

  • This time, we didn’t need to regroup because we had enough ones to subtract.
  • Now let’s try a problem where we might need to regroup: 52 minus 28 =?
  • Ask: How many tens are there in 52? (Answer: 5 tens).
  • How many ones are there in 52? (Answer: 2 ones).
  • Build 52 with 5 tens blocks and 2 ones blocks.
  • Subtracting ones:
    • We need to subtract 8 ones. Can we take 8 from 2? No!
    • So what do we do? Regroup!
    • Exchange 1 ten block for 10 ones.
  • Now we have 4 tens blocks and 12 ones blocks.
  • Continue subtraction. Subtract 8 ones from 12 ones. We are left with 4 ones.
  • Subtract 2 tens from 4 tens. We are left with 2 tens.
  • Conclusion:
    What’s left? 2 tens and 4 ones.
  • So, 52 – 28 = 24.

Reinforce:
We had to regroup because there weren’t enough ones. That’s okay – we simply trade one ten for ten ones!

You Do (Independent Practice):

Children work in pairs or individually with their own set of base ten blocks.
Give them problems such as

  • 53 – 21 =?
  • 71 – 46 =?
  • 64 – 28 =?

The teacher can ask guiding questions like, “Do you need to regroup? How many tens are you left with after borrowing?

Video: Base Ten Subtraction (with and without regrouping) – Coming soon

ISL Video: Base Ten Subtraction (with and without regrouping) – Coming soon

LTM: DIY Flashcards – Coming soon

LTM: Printable Flashcards – Coming soon

Activity 1: Subtraction Treasure Hunts

Objective: 
Children will apply their understanding of two-digit subtraction using base ten blocks in a game-like setting to reinforce learning in a fun and engaging way.

Importance of the activity for children:

Helps in developing:

  1. Gross motor skills (Moving around, running)
  2. Fine motor skills (Picking a card, hand-eye coordination, writing)
  3. Cognitive skills (Calculation, critical thinking)
  4. Social skills (Cooperation, playing together, discussing)
  5. Language skills (Articulating)
  6. Emotional skills (Builds confidence in numeracy, promotes a sense of achievement that boosts self-esteem, and encourages pride in learning new skills)

Resources required:

  1. Subtraction task cards (with and without regrouping)
  2. Base ten blocks (enough for each child or group)
  3. Envelopes or small containers labelled as ‘Treasure Boxes’
  4. Crayons or pencils
  5. Simple answer recording sheets

Setting for the activity:
The activity can be done indoors or outdoors with open floor space.

Type of activity: Individual or Pair activity

Preparation of activity:

  1. Prepare 6 to 10 subtraction task cards with visual cues (e.g., Use blocks to solve- 61 – 28).
  2. Place each card in an envelope with a small reward or sticker inside.
  3. Create an answer sheet with spaces labelled ‘Box 1’, ‘Box 2’, etc.
  4. Place base ten blocks at each station.

Role of the teacher: Demonstrator, observer and facilitator.

Procedure:

  1. Say: Today, we’re going on a Subtraction Treasure Hunt! Each treasure box has a problem inside. You’ll solve it using base ten blocks to unlock the treasure (a sticker or small surprise).
  2. Children go to each station, open the treasure box, take out the task card, and solve the subtraction problem using base ten blocks.
    1. They write the answer on their sheet in the correct box number.
    2. If they get it correct, they earn the sticker or surprise from that station.
    3. Then they go to the next box.
  3. Wrap-up Discussion: Bring children back together and ask:
    1. Which problems were easy? Which problems needed regrouping?
    2. How did the blocks help you figure it out?

Observations:
The teacher observes the children engaged in the activity to find:

  1. Are the children able to use base ten blocks correctly to model the subtraction problems?
  2. Do they demonstrate a good understanding of how to represent tens and ones?
  3. Are they able to identify when regrouping was needed in the problem?

Conclusion:
Children are able to solve two-digit subtraction using Base Ten blocks.

Video: Subtraction treasure hunt – Coming soon

ISL Video: Subtraction treasure hunt – Coming soon

Activity 2: Shape and Subtraction

Objective: 
Children will model and solve two-digit subtraction problems using clay to represent tens and ones, practicing regrouping when needed.

Importance of the activity for children:

Helps in developing:

  1. Gross motor skills (Bending, cleaning)
  2. Fine motor skills (Cutting, shaping, hand-eye coordination, writing)
  3. Cognitive skills (Calculation, critical thinking, spatial awareness)
  4. Social skills (Cooperation, playing together, discussing)
  5. Language skills (Articulating)
  6. Emotional skills (Builds confidence in numeracy, promotes a sense of achievement that boosts self-esteem, and encourages pride in learning new skills)

Resources required:

  1. Modelling clay or playdough (two colours preferred)
  2. Plastic knives or craft sticks (optional, for shaping)
  3. Subtraction problem cards (mix of with and without regrouping)
  4. Work mats or laminated place value mats (Tens and Ones)
  5. Wipes or paper towels for clean-up

Setting for the activity: 

  1. Children seated at desks or tables with space to model using clay.
  2. Materials ready in individual kits or trays.

Type of activity: Individual or Partner activity

Preparation of activity:

  1. Pre-roll some clay into long strips for quick access.
  2. Make a sample problem with clay to show the Modelling.
  3. Print or write subtraction problems on small cards (e.g., 54 – 28, 63 – 21)

Role of the teacher:

  1. Model how to use clay to create ‘tens rods’ and ‘ones cubes’.
  2. Explain how to ‘regroup’ by physically swapping 1 ten (a clay stick) for 10 ones (small clay balls).
  3. Guide children through a sample, then observe and assist as needed.
  4. Reinforce math vocabulary during the process: ‘tens’, ‘ones’, ‘regroup’, ‘subtract’.

Procedure:

Introduction:
Say, today, we’re going to subtract using clay! We’ll roll our own tens and ones, and even regroup when we need to by trading one ten for ten ones.

Demonstration (Teacher Models One):

  • Problem: 42 – 19 =?
  • Make 4 tens sticks and 2 ones balls using clay.
  • We need to take away 9 ones, but we only have 2. So we’ll trade 1 ten stick for 10 ones.
  • Swap one clay tens stick for 10 ones balls.
  • Now we have 3 tens sticks and 12 ones balls. Remove 9 ones balls and 1 ten stick. The result is 2 tens sticks and 3 ones balls.
  • So 42 – 19 = 23

Activity Time:

  • Children pick a card and model the first number using clay.
  • Check if regrouping is needed. If yes, swap a tens stick for 10 ones balls.
  • Subtract tens and ones physically.
  • Record their final answer on a worksheet or small whiteboard.

Suggested Variations:
Pair children and let one create the model while the other writes the number sentence and checks.

Observation:
The teacher observes the children engaged in the activity to find:

  1. Are children able to correctly create tens (clay rods) and ones (small balls) to model the numbers?
  2. Are they able to visually and physically distinguish between tens and ones?
  3. Are they able to demonstrate the process of exchanging 1 ten for 10 ones using clay?

Conclusion:
Children would learn subtraction through a hands – on activity.

Video: Shape and Subtraction – Coming soon

Video: Shape and Subtraction – Coming soon

Assessment

The teacher can give the practice worksheet to children that can be followed by an assessment worksheet.

Practice Worksheet – Coming soon

Practice Worksheet (Enlarged) – Coming soon

Assessment Worksheet – Coming soon

Assessment Worksheet (Enlarged) – Coming soon

Cross-Curricular Connection:

  • Language Class:
    Children write and illustrate short subtraction word problems based on real-life scenarios (e.g., “I had 45 apples. I gave 18 to my friend. How many are left?”
  • Art Class:
    Children can draw the answer to the math problem given. For example, the problem can be 20 -18 =? Children can draw two flowers or any two objects.
  • Physical Education Class:
    Children can play the ‘solve the subtraction problem and hunt the answer’ game. Children pick a problem chit from a box that contains as many chits as there are children, on which the problem is written. For example, a child picks up a chit that says 35 – 29 =? The child solves it, finds the answer to be six, and picks up any six objects around, like pebbles. The teacher can check for correctness.

Check list for teacher:

ActivityYesNoSometimes
Children can:
Understand the places in the number
Place the blocks or set of blocks in ones and tens places
Understand the word problems and solve them
Complete the activities in the given time
Do the activities independently
Express verbally and through actions, expressions, or gestures
Enjoy teamwork, appreciate others, and are willing to learn from others

Home Activity: Represent Using Wheat Dough Blocks

Show the following numbers using blocks made out of wheat dough, and find the difference. Take a picture and share it with the teacher.

  1. 16 – 10 = ?
  2. 18 – 16 = ?
  3. 47 – 28 = ?

Adaptations for addressing learner variability: Adaptations and strategies – Coming soon

Teacher Resource Document – Coming soon

Source and Attribution of images:
All images used in the above Assets and Aids are originally created.
This digital material has been developed by the Sri Sathya Sai Vidya Vahini Inclusive Education Project, a unit of Sri Sathya Sai Central Trust, Prasanthi Nilayam, as a collaborative offering in the service of our nation.