Grade: Grade 2 Subject: Mathematics Unit: Addition & Subtraction Within 1000 SAT: Algebra ACT: Math

Guided Practice

Learn

In this lesson, we will practice adding and subtracting three-digit numbers step by step. You will work through problems with hints and guidance to build your confidence.

Review: The Standard Algorithm

When adding or subtracting large numbers, we use the standard algorithm:

  1. Line up the digits by place value (ones under ones, tens under tens, hundreds under hundreds)
  2. Start with the ones place and work left
  3. Regroup (carry or borrow) when needed
  4. Write your answer with digits in the correct places

Tips for Success

  • Write neatly and keep columns straight
  • Check your work by using the opposite operation
  • Take your time with regrouping steps

Examples

Example 1: Addition with Regrouping

Problem: 347 + 285 = ?

Step 1: Add the ones: 7 + 5 = 12. Write 2, carry 1.

Step 2: Add the tens: 4 + 8 + 1 = 13. Write 3, carry 1.

Step 3: Add the hundreds: 3 + 2 + 1 = 6.

Answer: 632

Example 2: Subtraction with Regrouping

Problem: 524 - 168 = ?

Step 1: Subtract ones: 4 - 8? We need to borrow! Make it 14 - 8 = 6.

Step 2: Subtract tens: 1 - 6? Borrow again! Make it 11 - 6 = 5.

Step 3: Subtract hundreds: 4 - 1 = 3.

Answer: 356

Practice

Work through these problems. Use scratch paper to show your work.

1. 234 + 152 = ___

Hint: No regrouping needed! Add each column.

2. 456 + 278 = ___

Hint: You will need to regroup in the ones and tens places.

3. 389 + 247 = ___

Hint: 9 + 7 = 16. Write 6, carry 1.

4. 567 - 234 = ___

Hint: No borrowing needed! Subtract each column.

5. 742 - 385 = ___

Hint: Start with ones: 2 - 5. You need to borrow from tens.

6. 600 - 247 = ___

Hint: When borrowing from zeros, borrow across multiple places.

7. 483 + 299 = ___

Hint: Think of 299 as 300 - 1. Does that make it easier?

8. 815 - 479 = ___

Hint: You will need to borrow twice.

Check Your Understanding

Question 1: When do you need to regroup (carry) during addition?

Answer: When the sum of digits in a column is 10 or more.

Question 2: What should you do if you cannot subtract a larger digit from a smaller one?

Answer: Borrow 1 from the next column to the left, which adds 10 to your current column.

Question 3: How can you check if your answer to an addition problem is correct?

Answer: Use subtraction! Subtract one addend from your answer. You should get the other addend.

Question 4: What is 375 + 425?

Answer: 800

Next Steps

  • Practice a few more problems without looking at the hints
  • Try creating your own addition and subtraction problems
  • Move on to Word Problems to apply these skills to real situations