☰ Year plan · Mathematics

Even and odd numbers

Week 18 · Even and odd numbers · 3 lessons
2

Doubles are even

Discover Mathematics P2: Term 2, Lessons 71–80
GoalDouble a number and see that every double is even.
New words
double · a number added to itselfdoubles fact · an addition with two equal numbers, like 6 + 6sum · the answer to an addition
Explanation

To double a number, add it to itself. The double of 6 is 6 + 6 = 12. Two equal groups can always be paired up, one from each group, so a double has nothing left over. That means every double is an even number. Doubles of 1, 2, 3, 4 and 5 are 2, 4, 6, 8 and 10. Doubles of 6, 7, 8, 9 and 10 are 12, 14, 16, 18 and 20. You can use doubles for harder sums: 7 + 8 is one more than 7 + 7, so 7 + 8 = 15.

NumberDoubleEven or odd?
33 + 3 = 6even
55 + 5 = 10even
88 + 8 = 16even
Worked examples
+
Double 6: 6 + 6 = 12. Two groups of 6, and 12 is even.
Double 9: 9 + 9 = 18. The double of an odd number is even too.
Use a double: 7 + 8 is one more than 7 + 7. 7 + 7 = 14, so 7 + 8 = 15.
Class activity

Mirror doubles. Put a small mirror next to 5 buttons. How many buttons do you see now? Write the doubles sentence. Try with 3, 4 and 6 buttons. Are all the totals even?

Practice
1
What is the double of 7?
2
What is the double of 12?
3
Two baskets each hold 13 oranges. How many oranges in all? Is the number even or odd?
4
Which number is not a double: 14, 15 or 16?
5
Use a double to find 6 + 7.
+