☰ Year plan · Mathematics

Even and odd numbers

Week 18 · Even and odd numbers · 3 lessons
3

Odd plus odd, even plus even

Discover Mathematics P2: Term 2, Lessons 71–80
GoalPredict whether a sum is even or odd before adding.
New words
rule · something that is true every timepredict · to say the answer before you work it outsum · the answer to an addition
Explanation

Even numbers have no one left over. Odd numbers have one left over. Even + even: no ones left over, so the sum is even, like 4 + 6 = 10. Odd + odd: each number has one left over and those two join to make a pair, so the sum is even, like 3 + 5 = 8. Even + odd: one is left over, so the sum is odd, like 4 + 3 = 7. You can use these rules to predict a sum before adding, and to check your answer.

AddingSum is…Example
even + eveneven4 + 6 = 10
odd + oddeven3 + 5 = 8
even + oddodd4 + 3 = 7
Worked examples
+
6 + 4: both even, so the sum is even. 6 + 4 = 10.
+
7 + 5: both odd, so the sum is even. 7 + 5 = 12.
9 + 4: one odd and one even, so the sum is odd. 9 + 4 = 13.
Class activity

Sum sort. Write 10 addition sentences with numbers up to 10 on cards, such as 3 + 7 or 5 + 6. Before you add, predict: even or odd? Then add and check. Put the cards into two piles: even sums and odd sums.

Practice
1
Without adding, is 8 + 12 even or odd?
2
Without adding, is 9 + 7 even or odd?
3
Without adding, is 5 + 8 even or odd?
4
Add 11 + 13 and tell if the sum is even or odd.
5
Habiba adds two numbers and gets an odd sum. One number is even. Is the other number even or odd?