2nd Grade Subtracting Within 100 Lesson (Free PDF)
This subtract within 100 lesson for 2nd Grade covers subtracting within 100 (Common Core 2.NBT.B.5, 2.NBT.B.9), with a free PDF to print.
Subtracting within 100 means taking one number from another when both are less than 100. When a column does not have enough ones, trade 1 ten for 10 ones, then subtract ones and tens. You can also count back, count up, or draw a bar model. Adding the difference back to the smaller number checks the answer.
Grade 2 · Common Core State Standards: 2.NBT.B.5, 2.NBT.B.9
Key facts in this subtract within 100 lesson
- Trade 1 ten for 10 ones when the ones on top are too few.
- The difference is the answer to a subtraction problem.
- Counting back and counting up both find the same difference.
- Check subtraction with addition: difference + smaller number = whole.
- A bar model shows a whole and two parts.
What does it mean to subtract within 100?
Subtracting tells how many are left, or how far apart two numbers are. Within 100 means every number in the problem is less than 100, so you work with tens and ones.
How do you subtract when there are not enough ones?
Take \(52 – 27\). The number 52 has 5 tens and 2 ones, but you cannot take 7 ones from 2 ones. Trade one ten for ten ones. The amount stays the same, only the names change.
- Write 52 as 5 tens and 2 ones.
- Not enough ones, so trade 1 ten for 10 ones. Now 52 is 4 tens and 12 ones.
- Subtract the ones: \(12 – 7 = 5\).
- Subtract the tens: \(4 – 2 = 2\).
- The answer is \(25\). Check: \(25 + 27 = 52\).
What other strategies can you use?
Count back. To find \(63 – 28\), start at 63, jump back 20, then back 8.
Count up. To find \(71 – 46\), start at 46 and count up to 71. The jumps add to the difference.
Use a bar model. A bar model shows a whole and its two parts. If the whole is 84 and one part is 37, the other part is \(84 – 37\).
| Strategy | Works well when |
|---|---|
| Trade a ten | the ones digit on top is smaller |
| Count back | the number taken away is small |
| Count up | the two numbers are close together |
Why do these strategies work?
Trading keeps the total the same: 1 ten is worth exactly 10 ones. Counting back removes the number in two easy pieces: \(28 = 20 + 8\). Counting up works because the jumps fill the gap between the two numbers, and that gap is the difference. Addition always checks subtraction.
Subtract within 100 lesson: questions and answers
What does regrouping mean in subtraction?
Regrouping means trading one ten for ten ones so there are enough ones to subtract. The number does not change. For example, 41 is 4 tens and 1 one, or 3 tens and 11 ones.
How do I know when to trade?
Look at the ones. If the ones digit on top is smaller than the ones digit below it, trade 1 ten for 10 ones first. In 63 – 28, 3 is less than 8, so trade.
How can I check a subtraction answer?
Add the answer to the number you took away. If you get the starting number, the answer is right. For 71 – 46 = 25, check 25 + 46 = 71.
Is counting up the same as subtracting?
Yes. Counting up finds how far it is from the smaller number to the larger number. That distance is the difference, so both ways give the same answer.
Why can two strategies give the same answer?
Every correct strategy keeps the amounts equal, so the difference does not change. Trading, counting back, and counting up are different paths to the same number.
How to use this subtract within 100 lesson
Read the definitions first, then follow the worked method line by line and redo the example on paper without looking. When every step makes sense, move on to the worksheet, then check yourself with the quiz.
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All Grade 2 chapters: Grade 2 math.
