In Grade 2 you get faster and smarter with facts up to 20. Instead of counting one by one, you will use strategies: doubles, making ten, and fact families. Let’s build your math toolbox!
1. Doubles and Near Doubles
A doubles fact adds a number to itself, like \(6+6=12\). Doubles are easy to remember, and they help you with many other facts.
A double is a number added to itself: \(8+8=16\). A near double is two numbers that are 1 apart, like \(8+9\). Use the double you know, then add or subtract 1.
Find \(7+8\). Think: \(7+7=14\), and 8 is one more than 7, so \(7+8=14+1=15\).
2. The Making Ten Strategy
Ten is a friendly number. To add \(8+5\), first make a ten: \(8\) needs \(2\) more to reach \(10\). Split the 5 into \(2+3\).
- Start with the bigger number (here 8).
- Find how many more make 10 (here 2).
- Break the other number into that part and what is left (here \(5=2+3\)).
- Add the ten and the rest: \(10+3=13\).
Find \(9+6\). Take 1 from the 6 to make \(9+1=10\). What is left is 5. So \(9+6=10+5=15\).
3. Adding Three Numbers
You can add three numbers in any order. The sum stays the same! Look for two numbers that make ten, or for a double, and add those first.
You can add numbers in any order and the sum stays the same: \(4+9=9+4\) and \(3+5+7=7+3+5\).
Find \(6+7+4\). Spot \(6+4=10\). Then \(10+7=17\). So \(6+7+4=17\).
Do not forget the third number. After \(6+4=10\), you still need to add the 7.
4. Related Facts and Fact Families
Addition and subtraction are opposites. They undo each other. Three numbers can make a whole fact family.
A fact family uses the same three numbers. For 7, 8, and 15: \(7+8=15\), \(8+7=15\), \(15-7=8\), and \(15-8=7\). The whole (15) is the biggest number.
When a subtraction is hard, turn it into an addition. For \(15-8\), ask: “What goes with 8 to make 15?” Since \(8+7=15\), the answer is 7.
5. Missing Addend Problems
A missing addend is a part you do not know yet, like \(9+\square=16\). Count up from 9 to 16, or use subtraction: \(16-9=7\).
- Find the whole and the part you know.
- Count up from the part to the whole, or subtract: whole minus part.
- Check by adding: \(9+7=16\).
Lena has 8 shells. She wants 15. How many more does she need? Solve \(8+\square=15\). Since \(15-8=7\), she needs 7 more shells.
The fact family triangle for 6, 9, and 15 shows the same idea: if you cover one number at the bottom, you can find it from the other two.
6. Even and Odd Numbers
An even number can be split into two equal groups or into pairs with nothing left. An odd number always has one left over.
Even numbers end in 0, 2, 4, 6, or 8. Odd numbers end in 1, 3, 5, 7, or 9. A double is always even: \(6+6=12\).
On my planet we pair up space rocks! If every rock has a buddy, the number is even. If one rock is alone, it is odd.
7. Mental Math Strategies
Good mathematicians pick the strategy that fits the numbers. Here is a quick guide.
| Numbers look like… | Strategy | Example |
|---|---|---|
| Same number twice | Doubles | \(9+9=18\) |
| Numbers 1 apart | Near doubles | \(6+7=6+6+1=13\) |
| One number close to 10 | Make ten | \(9+4=10+3=13\) |
| A subtraction | Think addition | \(13-6\): \(6+7=13\), so 7 |
| A small number added | Count on | \(12+2=14\) |
Find \(17-9\). Think addition: \(9+8=17\), so \(17-9=8\).
Key takeaways
- A double adds a number to itself, and a near double is a double plus or minus 1.
- To make ten, move part of one addend to the other: \(8+5=10+3\).
- Three numbers can be added in any order, so look for ten first.
- Fact families use the same three numbers: two additions and two subtractions.
- To find a missing addend, count up or subtract the part from the whole.
- Even numbers make pairs with none left over, and odd numbers have one left over.
Test yourself: quick challenge for Grade 2
Speed drill for Grade 2: how many in 60 seconds?
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