A double is two groups that are exactly the same size.
Double means adding a number to itself, like 6 + 6.
Step 1: Let's Learn
Read it, or press Listen and follow the words.
Why doubles are worth knowing
Doubles are easy to picture, so they are easy to remember. Once you know them, they help you with everything else.
Every double gives an even answer. Two equal groups always share out evenly.
Two rows that match
Four in the top row. Four in the bottom row. The rows match exactly. That is what makes it a double. 4 + 4 = 8 A double is never worth counting out. It is worth knowing.
Step 2: Try It Yourself
Set both parts to the same number and watch the total.
First group and Second group
6
6
Double
12
6 and 6 make 12.
First group
Second group
How many in all
How many
12 and 8 make 20. There are 8 empty spaces.
6 and 6 make 12.
Step 3: In Real Life
A dozen eggs
A dozen eggs is two rows of 6. 6 + 6 = 12. A double. Two rows the same size are everywhere: shoes, eyes, the wheels on a car.
Step 4: Watch an Example
One step at a time.
Watch Ana Use a Double
Ana is asked for 7 + 7.
- Step 1
She sees a double right away. Both parts are 7.
First 7Second 7First 7Second 7
Watch Sam Use a Double
Sam is asked for 6 + 6. He starts. You finish.
- Step 1
He sees a double. Both parts are 6.
First 6Second 6First 6Second 6
Step 5: Your Turn
Practice makes it stick.
Two Hands
Problem 1 of 14
Leo has 8 marbles in each hand. How many marbles does he have in all?
marbles
Twin Bookshelves
Problem 2 of 14
Two shelves each hold 9 books. How many books are there in all?
books
Say the Doubles
Do not count. Picture the two equal groups.
Problem 3 of 14
5 + 5 = ?
Problem 4 of 14
6 + 6 = ?
Problem 5 of 14
8 + 8 = ?
Problem 6 of 14
10 + 10 = ?
Find the Mistake
A friend worked out a double. Can you spot the slip?
Problem 7 of 14
Kai adds 4 + 4. He says 9. What did Kai do?
Problem 8 of 14
What should Kai get for 4 + 4?
Problem 9 of 14
Max says 6 + 7 is a double. What did Max miss?
Problem 10 of 14
Max keeps the 6. 6 + ? is a double. What is the missing number?
Which Way?
Pick the quicker way for this sum.
Problem 11 of 14
8 + 8. Which way is quicker?
Problem 12 of 14
10 + 10. Which way is quicker?
Build Every Double
Set both parts the same. Build every double up to 10 + 10.
Problem 13 of 14
One part and The other part
4
4
Double
8
4 and 4 make 8.
Show the Missing Part
Build it, then check.
Problem 14 of 14
12 is 6 and how many? Show that part.
How many
Step 6: Quick Check
Show what you know.
Question 1 of 2
7 + 7 = ?
Question 2 of 2
Which of these is a double?
Ready for more?Optional. Past the lesson, for anyone who wants it.
Stretch 1 of 1
A double makes 18. What number was doubled?
What You Learned
- A double adds a number to itself.
- Doubles are easy to picture, so they are easy to remember.
- Every double gives an even answer.
For the grown-up
This lesson is where the child recalls doubles facts to 10 + 10 and recognizes a double as two equal addends. Fluency within twenty is not speed for its own sake. Facts that come without thinking free up the working memory that the next four years of mathematics need, and a child recomputing 8 + 6 every time has nothing left over for the problem it sits inside.
Watch for finger counting that has gone underground — a pause, a glance away, lips moving. The strategy has not gone; it has just got quieter.
Short and often beats long and rare. Two minutes of the facts they nearly know is worth more than twenty minutes of the ones they already do.
Why doubles are worth memorizing — A double is an addition fact where both numbers are the same: 4 + 4, 7 + 7, 9 + 9. There are only ten of them to learn, and once they are in your head they come back instantly, without counting. That speed is the whole point. Every other fact you meet can be reached from a double in one small step, so ten memorized facts do the work of far more.
Doubles you can already see — Your hands are 5 + 5. A pair of shoes is 1 + 1. An egg box holds 6 + 6. A week is 7 + 7 for two weeks. A month has about 15 + 15 days. When you meet a double you cannot recall, look for the thing in the world that shows it — the picture is easier to remember than the numbers.
Checking a double — Every double gives an even answer. Always. If you work out 6 + 6 and get 13, you can stop and try again before anyone tells you, because 13 is odd and a double can never be odd. This is your first taste of checking an answer using a rule rather than by redoing the work.