Subtraction Within 100

Grade 2 · mathematics · 100 practice problems · read aloud

🔊 Listen to this explanation

Subtraction Within 100

🧮 What is Subtraction?

Subtraction is like taking away or finding the difference between two numbers. We use it all the time! For example, if you have 15 stickers and give 7 to a friend, subtraction helps you find out how many you have left.

📝 How to Solve Subtraction Problems

Let's learn the Standard Algorithm (a fancy name for stacking numbers)!

  1. Write it down: Write the bigger number on top of the smaller number. Line up the ones and tens places.
  2. Subtract the Ones: Start with the column on the right. Subtract the bottom number from the top number.
  3. Subtract the Tens: Move to the left column. Subtract the bottom number from the top number.
  4. Write the Answer: You've got your answer!

🔍 Let's Look at Examples

Example 1: 48 - 25

Step 1: Stack the numbers.
  4 8
- 2 5
--------

Step 2: Subtract ones: 8 - 5 = 3

Step 3: Subtract tens: 4 - 2 = 2

Step 4: Answer: 23

Example 2: 52 - 17 (This one is trickier!)

Step 1: Stack the numbers.
  5 2
- 1 7
--------

Step 2: Uh-oh! Can't do 2 - 7. We need to regroup!

Step 3: Regroup from the tens. Take 1 ten from the 5, making it 4. Give that 1 ten (or 10 ones) to the 2, making it 12.
  5⁴12 2
- 1   7
--------

Step 4: Subtract ones: 12 - 7 = 5

Step 5: Subtract tens: 4 - 1 = 3

Step 6: Answer: 35

⚠️ Common Mistakes to Avoid

  • Forgetting to Regroup: Always check the ones column first! If the top number is smaller, you MUST regroup.
  • Subtracting the Top from the Bottom: Remember, you always subtract the bottom number from the top number.
  • Misaligning Numbers: Make sure the ones and tens places are lined up neatly so you subtract the right digits!

💡 Tips & Tricks

  • Keywords: Look for words like "take away", "how many are left", "difference", and "fewer". These often mean subtract!
  • Check with Addition: The best way to check your answer is to add it to the number you subtracted. If you get the original number, you're right! (e.g., 35 + 17 should equal 52).
  • Use a Number Line: Hop backward to find the answer. For 15 - 7, start at 15 and hop back 7 times. Where do you land?

🎯 How to Practice

You can get better at subtraction by practicing a little every day!

  • Use flashcards with and without regrouping.
  • Play online math games that focus on subtraction.
  • Solve word problems. Ask your teacher or parent for some, or make up your own!
  • Teach someone else how to do it. Teaching is a great way to learn!

Practice problems

6 of the 100, worked through step by step — try them before opening the answer.

1 12 - 8 = ?

Hint: Subtract the ones first, then the tens, borrowing if needed.

Show the answer

Answer: 4

  1. Start with 12.
  2. Subtract 8: 12 - 8 = 4.

The answer is 4.

2 72 - 38 = ?

Hint: Think about subtracting the tens first, then the ones. If you need to, you can regroup from the tens place.

Show the answer

Answer: 34

  1. Write the problem vertically in your mind: 72 - 38
  2. Start subtracting from the rightmost column (ones place). In 72, the ones digit is 2. In 38, the ones digit is 8. Since 2 is smaller than 8, we cannot subtract directly.
  3. We need to borrow from the tens place. The 7 in the tens place of 72 means 7 tens, which is 70. Take 1 ten from the 7 tens, leaving 6 tens. That 1 ten equals 10 ones. Add these 10 ones to the existing 2 ones: 10 + 2 = 12 ones.
  4. Now subtract the ones column: 12 ones - 8 ones = 4 ones. Write down 4 in the ones place of the answer.
  5. Move to the tens column. After borrowing, the tens digit of 72 is now 6 (not 7). Subtract the tens: 6 tens - 3 tens = 3 tens. Write down 3 in the tens place of the answer.
  6. Combine the digits: 3 tens and 4 ones gives 34. Therefore, 72 - 38 = 34.

Let's solve 72 - 38 step by step.

3 73 - 28 = ?

Hint: Think about breaking apart the numbers to make subtracting easier. You can use place value to help.

Show the answer

Answer: 45

  1. Write the problem vertically in your mind: 73 - 28
  2. Start with the ones column (rightmost digits): 3 - 8. Since 3 is smaller than 8, we cannot subtract directly. We need to borrow from the tens column.
  3. Borrow 1 from the 7 in the tens column. The 7 becomes 6, and the 3 in the ones column becomes 13 (because 1 ten = 10 ones, so 10 + 3 = 13).
  4. Now subtract in the ones column: 13 - 8 = 5. Write down 5 in the ones place of the answer.
  5. Move to the tens column: We now have 6 (after borrowing) - 2 = 4. Write down 4 in the tens place of the answer.
  6. Combine the digits: The tens digit is 4 and the ones digit is 5,

Let's solve 73 - 28 step-by-step. so the answer is 45. Final check: 73 - 28 = 45 is correct because 45 + 28 = 73. ANSWER: 45

4 45 - 18 = ?

Hint: Think about breaking apart the number you are subtracting to make it easier.

Show the answer

Answer: 27

  1. Write the problem vertically in your mind, aligning the digits by place value (ones and tens). 45 - 18
  2. Start by subtracting the numbers in the ones column (rightmost column). We have 5 - 8. Since 5 is smaller than 8, we cannot subtract directly. We need to borrow from the tens column.
  3. Borrow 1 ten from the 4 in the tens column. 1 ten is the same as 10 ones. So, the 4 in the tens place becomes 3 (because we borrowed 1), and the 5 in the ones place becomes 15 (5 + 10). So now we have: Tens column: 3 (after borrowing) Ones column: 15
  4. Now subtract the ones column: 15 - 8 = 7. Write down 7 in the ones place of the answer.
  5. Now subtract the tens column: 3 - 1 = 2. Write down 2 in the tens place of the answer.
  6. Combine the digits from the tens and ones columns: 2 and 7 gives 27. So, 45 - 18 = 27.

Let's solve 45 - 18 step-by-step.

5 75 - 28 = ?

Hint: Think about how you can break apart the numbers to make subtracting easier. You might want to adjust one of the numbers to create a friendlier problem.

Show the answer

Answer: 47

  1. Write the numbers vertically in your mind (align by place value): 75 - 28
  2. Start with the ones column: 5 - 8. Since 5 is smaller than 8, we cannot subtract directly. We borrow 1 from the tens column of 75.
  3. Borrowing 1 from the 7 in the tens column: The 7 becomes 6, and the 5 in the ones column becomes 15 (because 10 + 5 = 15). Now the problem in the ones column is: 15 - 8 = 7. Write down 7 in the ones place of the answer.
  4. Move to the tens column: We now have 6 (after borrowing) minus 2 = 4. Write down 4 in the tens place of the answer.
  5. Combine the results: Tens: 4, Ones: 7 → 47. Final answer: 47.

We are solving 75 - 28.

6 45 - 28 = ?

Hint: Think about how you can break apart the numbers to make subtracting easier. Consider using place value.

Show the answer

Answer: 17

  1. Write the problem vertically in your mind: 45 - 28
  2. Start with the ones column (rightmost digits): 5 - 8. Since 5 is smaller than 8, we cannot subtract directly. We need to borrow from the tens column.
  3. Borrow 1 ten from the 4 in the tens column. The 4 in the tens column becomes 3 (because we took 1 ten away). The 1 ten we borrowed equals 10 ones. We add these 10 ones to the existing 5 ones in the ones column. So now the ones column has: 10 + 5 = 15 ones.
  4. Now subtract the ones column: 15 - 8 = 7. Write down 7 in the ones place of the answer.
  5. Move to the tens column. After borrowing, the tens column originally had 4, but now it has 3 (because we borrowed 1 ten for the ones column). So we have 3 - 2 = 1. Write down 1 in the tens place of the answer.
  6. Combine the digits from tens and ones:

Let's solve 45 - 28 step-by-step. The answer is 17. Final check: 45 - 28 = 17 is correct because 17 + 28 = 45. ANSWER: 17

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