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Review: sums up to 20
Joyful Mathematics: Chapters 5–7
GoalAdd and take away with numbers up to 20.
New words
make ten · fill the ten firstcount on · say the next numberstake away from 20 · subtract from bigger numbers
Explanation
Remember the tricks. To add 9 + 6, fill the ten first: 9 and 1 make 10, and 5 more make 15. To add 13 + 5, start at 13 and count on 5: 14, 15, 16, 17, 18. To take away, cross out things and count the rest.
Worked examples
13 + 5 = 18. Count on from 13.
16 − 4 = 12. Four stars are crossed out.
13 + 7 = 20. 7 more dots fill the second frame.
Class activity
Bag of twenty. Put 20 small things in a bag, such as beans or stones. Take out a handful. Count them and say how many are left in the bag. Put them back and try again. Say the take-away sentence each time.
Practice
1
How many dots altogether?
14.
2
Start at 12. Count on 7. Where do you land?
19.
3
What is 17 − 5?
12.
4
Sana has 15 shells. She gives 8 to her sister. How many shells are left?
7.
5
Fill in: 11 + ___ = 20
9.