№ 742.
12/15 = (12:3)/(15:3) = 4/5 = (4·2)/(5·2) = 8/10 = 0,8
21/35 = (21:7)/(35:7) = 3/5 = (3·2)/(5·2) = 6/10 = 0,6
12/30 = (12:6)/(30:6) = 2/5 = (2·2)/(5·2) = 4/10 = 0,4
45/50 = (45:5)/(50:5) = 9/10 = 0,9
18/90 = (18:18)/(90:18) = 1/5 = (1·2)/(5·2) = 2/10 = 0,2
56/80 = (56:8)/(80:8) = 7/10 = 0,7
9/12 = (9:3)/(12:3) = 3/4 = (3·25)/(4·25) = 75/100 = 0,75
21/60 = (21:3)/(60:3) = 7/20 = (7·5)/(20·5) = 35/100 = 0,35
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Или так:
12/15 = 12 : 15 = 0,8
21/35 = 21 : 35 = 0,6
12/30 = 12 : 30 = 0,4
45/50 = 45 : 50 = 0,9
18/90 = 18 : 90 = 0,2
56/80 = 56 : 80 = 0,7
9/12 = 9 : 12 = 0,75
21/60 = 21 : 60 = 0,35