Subtraction - One Digit | Second Grade
What is Subtraction?
Concept: Subtraction means taking away, finding the difference, or comparing groups. We use the minus sign (−) to show subtraction.
Subtraction Terms:
9 − 4 = 5
• Minuend: 9 (the number we start with)
• Minus Sign (−): Means "subtract" or "take away"
• Subtrahend: 4 (the number being taken away)
• Equals Sign (=): Means "the same as"
• Difference: 5 (the answer)
💡 Tip: Subtraction makes numbers smaller! Think "How many are left?"
1. Subtract One-Digit Numbers (Up to 10)
Concept: When we subtract one-digit numbers and start with 10 or less, these are our basic subtraction facts!
Subtraction Facts from 10
10 − 0 = 10
10 − 1 = 9
10 − 2 = 8
10 − 3 = 7
10 − 4 = 6
10 − 5 = 5
10 − 6 = 4
10 − 7 = 3
10 − 8 = 2
10 − 9 = 1
10 − 10 = 0
Relationship with Addition:
Subtraction and addition are opposite operations!
If \( 3 + 7 = 10 \), then:
• \( 10 − 7 = 3 \)
• \( 10 − 3 = 7 \)
💡 Tip: Use addition facts to check your subtraction! If 8 − 5 = 3, then 3 + 5 = 8
2. Ways to Subtract
Concept: There are different strategies to help you subtract! Choose the method that works best for you.
Subtraction Strategies
Strategy 1: Count Back
Example: 8 − 3 = ?
Start at 8, count back 3 times: 7, 6, 5
Answer: 5
Strategy 2: Use Objects
Example: 7 − 4 = ?
⭕⭕⭕⭕⭕⭕⭕
Cross out 4 objects
❌❌❌❌⭕⭕⭕
Answer: 3 left
Strategy 3: Number Line
Example: 9 − 5 = ?
Start at 9, jump back 5 spaces
0---1---2---3---4---5---6---7---8---9
←←←←← Jump back 5
Answer: 4
Strategy 4: Think Addition
Example: 6 − 2 = ?
Think: "2 plus what equals 6?"
2 + ? = 6
2 + 4 = 6
Answer: 4
💡 Tip: Try different strategies and use the one that's easiest for each problem!
3. Subtract Doubles
Concept: When we subtract a number from its double, the answer is always the same as the number we subtracted!
Doubles Subtraction Pattern
If you know: \( n + n = 2n \)
Then: \( 2n − n = n \)
Doubles Subtraction Facts
2 − 1 = 1
Double 1
4 − 2 = 2
Double 2
6 − 3 = 3
Double 3
8 − 4 = 4
Double 4
10 − 5 = 5
Double 5
12 − 6 = 6
Double 6
14 − 7 = 7
Double 7
16 − 8 = 8
Double 8
18 − 9 = 9
Double 9
💡 Tip: If you know addition doubles, you automatically know subtraction doubles!
4. Subtract One-Digit from Two-Digit (Up to 18)
Concept: We can subtract a one-digit number from numbers like 11, 12, 13... up to 18!
📝 Examples
Example 1: 15 − 7 = ?
Method 1: Think of 15 as 10 + 5
First subtract 5: 15 − 5 = 10
Then subtract 2 more: 10 − 2 = 8
15 − 7 = 8
Example 2: 13 − 6 = ?
Method 2: Think addition
6 + ? = 13
6 + 7 = 13
13 − 6 = 7
💡 Tip: Break down the subtraction into easier steps - subtract to 10 first!
5. Subtraction with Pictures
Concept: Pictures help us see subtraction! Count what's left after taking some away or crossing out.
📝 Visual Example
8 stars, cross out 3. How many left?
⭐⭐⭐⭐⭐⭐⭐⭐
↓ Cross out 3 ↓
❌❌❌⭐⭐⭐⭐⭐
Started with 8 stars
Crossed out 3 stars
Count what's left: 5 stars
8 − 3 = 5
💡 Tip: Draw pictures or use objects when solving subtraction problems!
6. Subtraction Input/Output Tables (Up to 18)
Concept: In input/output tables, we subtract the same number from each input to get the output!
📝 Example: Subtract 4 from each number
| Input | Rule: − 4 | Output |
|---|---|---|
| 10 | 10 − 4 | 6 |
| 12 | 12 − 4 | 8 |
| 15 | 15 − 4 | 11 |
| 18 | 18 − 4 | 14 |
💡 Tip: Find the rule (what's being subtracted), then apply it to each input!
7. Subtract Zero or Subtract All
Concept: Two special subtraction rules that are easy to remember!
Subtract Zero
\( a − 0 = a \)
Subtracting zero doesn't change the number!
7 − 0 = 7
12 − 0 = 12
18 − 0 = 18
Subtract All
\( a − a = 0 \)
When you subtract everything, nothing is left!
5 − 5 = 0
9 − 9 = 0
14 − 14 = 0
💡 Tip: These are the easiest subtraction problems - learn them first!
8. Subtraction Word Problems (Up to 18)
Concept: Word problems tell a story with subtraction. Look for keywords like "left," "fewer," "difference," and "take away."
Subtraction Keywords:
✓ take away
✓ left
✓ remain
✓ fewer
✓ difference
✓ how many more
📖 Example Problem
Tom had 12 candies. He gave 5 candies to his sister. How many candies does Tom have left?
Solution Steps:
Step 1: Find the numbers (12 and 5)
Step 2: Look for keywords ("left" = subtract)
Step 3: Write the equation: 12 − 5 = ?
Step 4: Solve: 12 − 5 = 7
Answer: Tom has 7 candies left
💡 Tip: Draw a picture or act out the problem to understand it better!
9. Balance Subtraction Equations (Up to 18)
Concept: An equation is balanced when both sides are equal. Both sides must have the same value!
Balance Concept:
\( 10 − 3 = 12 − 5 \)
Left side: 10 − 3 = 7
Right side: 12 − 5 = 7
Both sides equal 7 ✓ BALANCED!
📝 Practice: Find the Missing Number
\( 15 − 6 = 18 − ? \)
Left side: 15 − 6 = 9
Right side must also equal 9
18 − ? = 9
So ? = 9
Answer: 9
💡 Tip: Solve one side first, then find what makes the other side equal to it!
Important Subtraction Formulas
Subtraction-Addition Relationship
If \( a − b = c \)
Then \( c + b = a \)
9 − 5 = 4
So 4 + 5 = 9
Subtract Zero
\( a − 0 = a \)
8 − 0 = 8
Number stays the same!
Subtract All
\( a − a = 0 \)
7 − 7 = 0
Nothing left!
🎯 Tips for Subtraction Success 🎯
- ✓ Use addition facts to help with subtraction - they're related!
- ✓ Count back on your fingers or a number line
- ✓ Draw pictures or use objects to see the subtraction
- ✓ Practice subtraction facts to 10 until you know them by heart
- ✓ In word problems, circle keywords that mean "subtract"
- ✓ Check your answer by adding back!
⭐ You're a Subtraction Star! ⭐
Excellent work mastering one-digit subtraction! You now know subtraction facts to 10 and beyond, can subtract from two-digit numbers, use pictures and number lines, solve word problems, work with input/output tables, balance equations, and understand special rules like subtracting zero. Subtraction is the opposite of addition, and knowing both makes you a math superstar! Keep practicing and you'll subtract faster and faster. You're doing fantastic!