Solved examples of decomposition strategy subtraction for Grade 3.

📚 Quick Study Guide

🔢 Decomposition: This is when you break down a number into smaller parts to make subtraction easier. For example, breaking down 42 into 30 + 12. 💡 When to Use: Use decomposition when the digit you are subtracting in the ones place is larger than the digit you are subtracting from. ✏️ Steps for Decomposition Subtraction:
1. Look at the ones place. If the digit you are subtracting from is smaller, you need to decompose.
2. Take 10 from the tens place and add it to the ones place.
3. Subtract the ones place.
4. Subtract the tens place.
5. Combine your answers!
➕ Example: Let's subtract 27 from 63.
• We can't subtract 7 from 3, so we decompose 63.
• 63 becomes 50 + 13.
• Now, subtract 7 from 13. $13 - 7 = 6$.
• Next, subtract 20 from 50. $50 - 20 = 30$.
• Finally, add the results: $30 + 6 = 36$. So, $63 - 27 = 36$.

🧪 Practice Quiz

1. What is the first step in decomposition subtraction when you can't subtract the ones digits?
1. Add the numbers.
2. Decompose the larger number.
3. Subtract the tens digits.
4. Carry over from the next column.
2. What does it mean to decompose a number?
1. To add a number to itself.
2. To break a number down into smaller parts.
3. To multiply a number by zero.
4. To divide a number by two.
3. Solve using decomposition: $52 - 25 = ?$
1. 37
2. 27
3. 33
4. 23
4. Solve using decomposition: $74 - 38 = ?$
1. 46
2. 36
3. 44
4. 34
5. Which of the following is an example of decomposing the number 85?
1. $80 + 8$
2. $70 + 15$
3. $50 + 35$
4. $60 + 20$
6. What two numbers do you subtract *after* decomposing 46 to solve $46 - 18$?
1. $16 - 8$ and $30 - 10$
2. $6 - 8$ and $4 - 1$
3. $16 - 10$ and $30 - 8$
4. $46 - 8$ and $46 - 10$
7. What is $91 - 64$ using decomposition subtraction?
1. 37
2. 27
3. 33
4. 23