Addition & Subtraction to 100
Learn how to add and subtract numbers up to 100 using number lines, columns, and bar models!
Adding on a Number Line
A number line helps us add by jumping forwards. To add a number, start at the first number and jump to the right.
Example: 23 + 14
Start at 23. Jump +10, then jump +4.
Subtracting on a Number Line
To subtract, we jump backwards (to the left). Example: 45 - 12. Start at 45. Jump back 10, then jump back 2.
Column Addition (No Regrouping)
We can also add by lining numbers up in columns. Add the ones first, then the tens.
Example: 32 + 45
Ones: 2 + 5 = 7
Tens: 3 + 4 = 7
Answer: 77
Bar Models for Word Problems
A bar model is a picture that helps us understand a word problem. It shows the whole and the parts.
Example: Tom has 24 stickers. He gets 13 more. How many does he have now?
WHOLE (what we want to find)
Part 1
Part 2
Add the parts: 24 + 13 = 37 stickers
Key Vocabulary
Addition
Putting numbers together to find the total. We use the + sign.
Subtraction
Taking a number away from another. We use the - sign.
Number Line
A line with numbers in order. We jump forwards to add and jump backwards to subtract.
Bar Model
A picture using bars to show the parts and the whole in a word problem.
Worked Examples
What is 35 + 23?
Step 1: Add the ones: 5 + 3 = 8
Step 2: Add the tens: 30 + 20 = 50
Answer: 50 + 8 = 58
What is 67 - 24?
Step 1: Subtract the ones: 7 - 4 = 3
Step 2: Subtract the tens: 60 - 20 = 40
Answer: 40 + 3 = 43
Mia has 41 marbles. She gives 20 to her friend. How many does she have left?
Step 1: This is a subtraction problem: 41 - 20.
Step 2: Subtract the tens: 40 - 20 = 20. The ones stay the same: 1.
Answer: Mia has 21 marbles left.
Knowledge Check
Choose the correct answer and press "Check Answer"!
Question 1
What is 24 + 35?
Question 2
What is 78 - 35?
Question 3
Sam has 52 sweets. He gets 26 more. How many sweets does Sam have now?
Question 4
What is 60 - 30?
Question 5
There were 85 birds in a tree. 43 flew away. How many birds are left?
Key Concepts Summary
- ● Use a number line to add (jump forward) or subtract (jump back).
- ● In column addition, add the ones first, then the tens.
- ● Bar models help us picture word problems by showing parts and the whole.
- ● Break big jumps into smaller ones: jump 10s first, then 1s.
- ● Always check: does your answer make sense?