1
Review: adding and subtracting within 20
Textbook: Part 1, lesson 1, pp. 4–5
GoalReview adding and subtracting within 20; finding sums and differences.
New words
sum (result of adding) · yig‘indidifference (result of subtracting) · ayirmavalue (of an expression) · qiymatchart · diagramma
Explanation
Adding gives a sum and subtracting gives a difference. Within 20 it helps to fill up to 10 first: 8 + 5 = 8 + 2 + 3 = 13. The number we get from an expression is called its value.
Worked examples
9 + 6: first fill 9 up to 10, so 9 + 1 + 5 = 15.
15 − 7: first take away 5, then 2 more: 15 − 5 − 2 = 8.
Class activity
“Autumn leaves”: six leaf cards with sums (8 + 5, 14 − 6 ...) are put on the board. Children come up in turns and write the answer under a leaf. The pair with most correct answers wins.
Practice
1
8 + 7 = ?
15
2
16 − 9 = ?
7
3
A branch has 6 yellow and 8 red leaves. How many in all?
14
4
In September 12 days were sunny and 7 were cloudy. How many more sunny days than cloudy?
5