Addition of 2 Digit Numbers

Week 1

Learning Outcome

Adds two-digit numbers up to 99 using place value concept and regrouping.

Objective

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

Prerequisites

Children can perform single-digit addition.

Pre-teach Vocabulary

Children should be familiar with the terms such as, place value, add, plus and equal to.

Introduction: Base Ten Addition

Materials required:

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

The teacher could begin by reviewing the topic of addition using a few objects. The teacher shows a basket containing 6 apples and puts 3 more apples in the basket and asks the children, how many apples are there in the basket now?

  • Now the children will be able to count the total apples in the basket and say the answer is 9. The teacher writes the answer on the board. 6+3 =9.
  • The teacher will show other available objects and repeat the exercise and familiarise the children with the concept of addition.
  • 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 add two-digit numbers using base ten blocks. Base ten blocks help us see the tens and ones clearly, so addition 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 add 23 to 45. I start with ones.
  5. Physically take 3 ones and put them with 5 ones.
  6. Count the total ones. It is 8.
  7. Now, physically take 2 tens and put them with 4 tens.
  8. Count the number of tens blocks. It is 6.
  9. So, 45 plus 23 equals 68.
  10. Say Aloud:
    1. I always start by looking at the ones. If I get more than ten when I count ones together, I may need to regroup ones into tens. If not I keep the total number of ones.
    2. Then I count the number of tens block to find the total number of tens
  11. Take 58+34 for instance
  12. Ask children: Let’s build 58 together. How many ones are there in the number 58? (Answer: 8). How many tens are there in the number 58? (Answer: 5). 

Work together:

  • Build 58.
  • Now, we need to add 34. Take 4 ones and put them with 8 and count. How many ones are there now? 12 ones are there.
  • No, so we need to regroup.
  • Exchange 1 ten for 10 ones. Now we have 6 tens and 2 ones.
  • Add 3 tens to 6 tens and count the tens together. We have 9 tens.
  • So we have 9 tens and 2 ones.
  • What is the answer? 9 tens and 2 ones = 92.
  • So, 58 + 34 = 92

We Do (Guided practice):

Let’s solve 46 plus 23 using base ten blocks. What do we do first?

  • Ask: How many ones are there in 46? (Answer: 6 ones)
  • Ask: How many tens are there in 46? (Answer: 4 tens)
  • Build 46 using 4 tens blocks and 6 ones blocks.
  • Now we have to add 23. That is 2 tens and 3 ones.
  • Physically put 6 ones and 3 ones and count them together. 
  • What is the total number of ones? It is 9 ones blocks. 
  • Is there a need to regroup? Answer: No
  • Physically put 2 tens block with 4 tens block and count them together.
  • What is the total number of tens? It is 6 tens blocks.
  • So the answer is 69.

Conclusion: 46 + 23 = 69.

Reinforce:

  • This time, we didn’t need to regroup because the total number of ones is less than 10.
  • Now let’s try a problem where we might need to regroup: 57 plus 28 =?
  • Ask: How many tens are there in 57? (Answer: 5 tens).
  • How many ones are there in 57? (Answer: 7 ones).
  • Build 57 with 5 tens blocks and 7ones blocks.
  • Add ones:
    • We need to add 8 ones with 7 ones. It is 15 ones which is greater than ten.
    • So what do we do? Regroup!
    • Exchange 1 ten block for 10 ones.
  • Now we have 6 tens blocks and 5 ones blocks.
  • Add 6 tens block to 2 tens block. It is 8 tens blocks.
  • So, in total we have 8 tens blocks and 5 ones blocks.

Conclusion: 57 + 28 = 85

Reinforce:
We had to regroup because the total number of ones is greater than 10. So, 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 = ?
  • 68 + 26 = ?
  • 49 + 28 = ?

The teacher can ask guiding questions like, “Do you need to regroup? How many ones do you have after counting the ones together?

Refer to ‘Executive Function skills’ Adaptations and Strategies given in the Main page of ‘Addition of 2 Digit Numbers’ if there are any neuro-diverse children in the class.

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

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

LTM: DIY Flashcards – Coming soon

LTM: Printable Flashcards – Coming soon

Activity 1: Addition Treasure Hunt

Objective: 
Children will apply their understanding of two-digit addition using base ten blocks in a game-like setting to reinforce learning the concept of addition 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. Addition 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 addition 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 an Addition Treasure Hunt! Each treasure box has a problem inside. You’ll solve it using base ten blocks to unlock the treasure (a sticker, a chocolate, or any other small surprise).
  2. Children go to each station, open the treasure box, take out the task card, and solve the addition 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, chocolate, 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 addition 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 addition using Base Ten blocks.

Refer to ‘Attention and Focus’ Adaptations and Strategies given in the Main page of ‘Addition of 2 Digit Numbers’ if there are any neuro-diverse children in the class.

Video: Addition treasure hunt – Coming soon

ISL Video: Addition treasure hunt – Coming soon

Activity 2: Shape and Add

Objective: 
Children will model and solve two-digit addition 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. Addition 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 addition 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,” “addition.”

Procedure:

Introduction:
Say, today, we’re going to learn how to add 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 add 9 ones with 2 ones. 
  • Physically put 9 ones clay balls with 2 ones clay balls and count the total number of ones clay balls. It is 11.
  • So we’ll trade 1 ten stick for 10 ones. 
  • Swap one clay tens stick for 10 ones balls. We are left with one clay ball.
  • Now we have 5 tens sticks and1 tens stick. Count them together. We have 6 tens sticks and 1 ones clay ball. The result is 6 tens sticks and 1 ones balls.
  • So 42 + 19 = 61.

Activity Time:

  • Children pick a card and model the first number using clay.
  • Then, model the number to be added with the first number using clay.
  • Proceed to add the two numbers.
  • Check if regrouping is needed. If yes, swap a tens stick for 10 ones balls.
  • Add 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 addition through a hands-on activity.

Video: Shape and Add – Coming soon

Video: Shape and Add – Coming soon

Assessment

The teacher can give the practice worksheet to children which 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 addition word problems based on real-life scenarios (e.g., I had 12 chocolates. My sister gave me 15 chocolates. How many chocolates do I have now?
  • Art Class:
    Children can draw the answer to the math problem given. For example, the problem can be 20 + 18 =? Children can draw the required number of any two objects in two columns and give the answer. Or the problem can be written on the board as 12 stars+18 stars =? Children can solve the problem and draw the answer (30 stars)
  • Physical Education Class:
    Children can play the ‘Solve the addition problem and match your answer with the answer chit box’ 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 64. Then goes to the answer chit box and picks a chit where the problem and answer (35+29=64) are written. The child then matches the answer written with their solution. The teacher guides if the answer is found to be wrong.

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 2-digit addition problems and solve them
Regroup ones blocks with tens blocks if required
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 total. Take a picture and share it with the teacher.

  1. 16 + 10 = ?
  2. 58 + 16 = ?
  3. 47 + 28 = ?

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.