Addition - One Digit | Second Grade
What is Addition?
Concept: Addition means putting numbers or groups together to find how many in all! We use the plus sign (+) to show addition.
Addition Terms:
3 + 5 = 8
• Addends: 3 and 5 (numbers being added)
• Plus Sign (+): Means "add"
• Equals Sign (=): Means "the same as"
• Sum: 8 (the answer)
💡 Tip: Addition makes numbers bigger! Think "How many altogether?"
1. Add One-Digit Numbers (Sums to 10)
Concept: When we add two one-digit numbers and get 10 or less, these are our basic addition facts!
Addition Facts to 10
| + | 0 | 1 | 2 | 3 | 4 | 5 |
|---|---|---|---|---|---|---|
| 0 | 0 | 1 | 2 | 3 | 4 | 5 |
| 1 | 1 | 2 | 3 | 4 | 5 | 6 |
| 2 | 2 | 3 | 4 | 5 | 6 | 7 |
| 3 | 3 | 4 | 5 | 6 | 7 | 8 |
| 4 | 4 | 5 | 6 | 7 | 8 | 9 |
| 5 | 5 | 6 | 7 | 8 | 9 | 10 |
Ways to Make 10:
0 + 10 = 10
1 + 9 = 10
2 + 8 = 10
3 + 7 = 10
4 + 6 = 10
5 + 5 = 10
💡 Tip: Memorize these facts! They're the building blocks for all addition.
2. Add Doubles
Concept: Doubles are when we add the same number to itself! Doubles are easy to remember and very useful.
Doubles Facts
1 + 1 = 2
Double 1
2 + 2 = 4
Double 2
3 + 3 = 6
Double 3
4 + 4 = 8
Double 4
5 + 5 = 10
Double 5
6 + 6 = 12
Double 6
7 + 7 = 14
Double 7
8 + 8 = 16
Double 8
9 + 9 = 18
Double 9
Doubles Pattern:
✓ All doubles give EVEN numbers
✓ Think of it as "2 groups of the same number"
✓ Formula: \( n + n = 2n \)
💡 Tip: Know your doubles! They help you solve other addition problems quickly.
3. Add Zero
Concept: When we add zero to any number, the number stays the same! Zero is the identity element for addition.
Zero Property of Addition
\( a + 0 = a \)
\( 0 + a = a \)
Adding zero doesn't change the number!
Examples:
0 + 5 = 5
7 + 0 = 7
0 + 9 = 9
3 + 0 = 3
0 + 0 = 0
💡 Tip: Zero means "nothing" - so adding nothing doesn't change anything!
4. Addition with Pictures (Sums to 20)
Concept: Pictures help us see addition! Count the objects in each group, then count them all together.
📝 Visual Example
How many apples in total?
🍎🍎🍎
3 apples
+
🍎🍎🍎🍎
4 apples
=
🍎🍎🍎🍎🍎🍎🍎
7 apples
Answer: 3 + 4 = 7
💡 Tip: Count each group, then count all together to find the sum!
5. Addition Input/Output Tables (Sums to 20)
Concept: Input/output tables show a pattern. We add the same number to each input to get the output!
📝 Example: Add 3 to each number
| Input | Rule: + 3 | Output |
|---|---|---|
| 2 | 2 + 3 | 5 |
| 4 | 4 + 3 | 7 |
| 5 | 5 + 3 | 8 |
| 7 | 7 + 3 | 10 |
💡 Tip: Find the rule (what's being added), then apply it to each input!
6. Addition Word Problems
Concept: Word problems tell a story with numbers. Look for keywords like "altogether," "in all," "total," and "plus."
Addition Keywords:
✓ altogether
✓ in all
✓ total
✓ plus
✓ more
✓ combined
📖 Example Problem
Sara has 4 balloons. Her friend gives her 3 more balloons. How many balloons does Sara have in all?
Solution Steps:
Step 1: Find the numbers (4 and 3)
Step 2: Look for keywords ("in all" = add)
Step 3: Write the equation: 4 + 3 = ?
Step 4: Solve: 4 + 3 = 7
Answer: Sara has 7 balloons
💡 Tip: Underline the numbers and circle the keyword to help you!
7. Balance Addition Equations
Concept: An equation is balanced when both sides are equal. Like a seesaw - both sides must have the same value!
Balance Concept:
\( 3 + 2 = 4 + 1 \)
Left side: 3 + 2 = 5
Right side: 4 + 1 = 5
Both sides equal 5 ✓ BALANCED!
📝 Practice: Find the Missing Number
\( 5 + 3 = 6 + ? \)
Left side: 5 + 3 = 8
Right side must also equal 8
6 + ? = 8
So ? = 2
Answer: 2
💡 Tip: Solve one side first, then make the other side equal to it!
8. Add Three or More One-Digit Numbers
Concept: We can add more than two numbers! Look for pairs that make 10 to make it easier.
Strategy: Make 10
Example: \( 7 + 5 + 3 + 5 \)
Step 1: Look for pairs that make 10
• 7 + 3 = 10 ✓
• 5 + 5 = 10 ✓
Step 2: Add the tens
• 10 + 10 = 20
Answer: 20
Strategies:
✓ Look for doubles (5 + 5, 4 + 4)
✓ Make 10 (7 + 3, 6 + 4, 8 + 2)
✓ Add from left to right
✓ Group easy numbers first
💡 Tip: You can add numbers in any order - find the easiest way!
9. Repeated Addition for Arrays
Concept: An array shows objects in rows and columns. We can use repeated addition to count them! This is the beginning of multiplication.
📝 Array Example
3 rows of 4 stars
★ ★ ★ ★
★ ★ ★ ★
★ ★ ★ ★
Row 1: 4 stars
Row 2: 4 stars
Row 3: 4 stars
Repeated Addition: 4 + 4 + 4
Answer: 12 stars
Array Formula:
Number of rows × Number in each row
OR
Add the same number repeatedly
💡 Tip: Arrays help you see groups! This is how we learn multiplication later.
Important Addition Formulas
Commutative Property
\( a + b = b + a \)
3 + 5 = 5 + 3
Order doesn't matter!
Identity Property
\( a + 0 = a \)
7 + 0 = 7
Adding zero changes nothing!
Associative Property
\( (a + b) + c = a + (b + c) \)
(2+3)+4 = 2+(3+4)
Group any way you want!
🎯 Tips for Addition Success 🎯
- ✓ Memorize addition facts to 10 - they're essential!
- ✓ Know your doubles - they make other facts easier
- ✓ Use your fingers or draw pictures when you need help
- ✓ Look for ways to make 10 - it's a powerful strategy
- ✓ In word problems, look for keywords that mean "add"
- ✓ Practice every day - addition gets faster with practice!
⭐ You're an Addition Champion! ⭐
Fantastic work mastering one-digit addition! You now know addition facts to 10 and beyond, can add with pictures, solve word problems, balance equations, add multiple numbers, work with arrays, and use powerful strategies like making 10 and using doubles. Addition is one of the most important math skills you'll ever learn. Keep practicing and you'll become lightning-fast at adding! You're doing amazing work!