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кажется так :) рисунок.
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1) 4\9 = 16\36
1\4 = 9\36
7\12 = 21\36
13\18 =26\36
1\4, 4\9, 7\12, 13\18
2) 28\45 = 56\90
5\9=50\90
7\10 = 63\90
13\18=65\90
8\15 =48\90
8\15, 5\9, 28\45, 7\10, 13\18