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Adding up to twenty
Discover Mathematics: Chapter 7
GoalAdd two numbers with a total up to 20, by making ten or by counting on.
New words
total · all of them togethermake ten · fill a ten-frame firstcount on · start at the bigger number and count upequals · has the same value as
Explanation
There are two ways to add numbers that go past ten. The first way is to make ten. To add 8 + 5, fill the first ten-frame with 8, then move 2 dots from the 5 to fill it. The ten-frame is full with 10, and 3 dots are left. So 10 + 3 = 13. The second way is to count on. Start at 8 and count on five more: 9, 10, 11, 12, 13.
Worked examples
To add 9 + 6, take 1 from the 6 to make 10 with the 9. Then 10 + 5 = 15.
To add 7 + 4, start at 7 and count on 4: 8, 9, 10, 11. So 7 + 4 = 11.
Laila picks 6 tulips and 7 roses. 6 + 7 = 13, so she has 13 flowers.
Class activity
Ten-frame drawing. Draw two ten-frames on paper, each with 2 rows of 5 boxes. Give a sum such as 7 + 6. The child draws 7 dots in the first frame and 6 dots after them, then counts the total. Try 8 + 7 and 9 + 5.
Practice
1
Add: 7 + 6. Look at the ten-frames.
13
2
What is 8 + 4?
12
3
Start at 9 and count on 3. Where do you stop?
12
4
Ziad has 9 sweets. His aunt gives him 5 more. How many sweets does he have?
14
5
What is 10 + 6?
16