1. .
2. :
5 6 7.
15 11 7.
6 4 8.
13 9 8.
17 2 5.
3. . 60 7 . ?
II. .
.
= 15.
1. .
: ) 12 + 3 = 15 ) 16 1 = 15 ) 9 + 6 = 15
) 18 3 = 15 ) 10 + 5 = 15
? (9 + 6 = 15.)
2. .
, 15.
: 9 + 3 = 12; 9 + 6 = 15.
3. ? ? .
:
1) 9 + 6 = 15 (.) .
2) 15 3= 12 (.) .
4. . , 7 + 8.
7 + 8 = 7 + (3 + 5) = (7 + 3) + 5 = 10 + 5 = 15.
: 7 + 8 = 15.
:
1) 8 1 = 7 (.) .
2) 8 + 7 = 15 (.) .
6. , 12, , 15. .
8 + 4 = 12 8 + 7 = 15
9 + 3 = 12 9 + 6 = 15
7 + 5 = 12 7 + 8 = 15
6 + 6 = 12 6 + 9 = 15
7. ? ? .
: 1) 15 1 = 14 (.);
2) 14 = 7 + 7 (.) ;
3) 7 + 1 = 8 (.) .
8. , , 10 . . .
10 1 = 9 10 3 = 7 10 4 = 6
10 7 = 3 10 9 = 1 10 6 = 4
III. .
,
21
18
: = 18; .
.
: 20 18, (, ) (, , ); .
: ; , .
( / ): : ( , ); ; : , ( ) , , ; ; : , ; , , .
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