5 7/8 + 2 1/12 = 5 21/24 + 2 2/24 = 7 23/24
10 - 7 5/9 = 9 9/9 - 7 5/9 = 2 4/9
1 53/14 - 4 1/21 = 1 + 3 11/14 - 4 1/21 = 4 11/14 - 4 1/21 = 4 33/42 - 4 2/42 = 31/42
7 1/9 - 5 7/12 = 7 4/36 - 5 21/36 = 6 40/36 - 5 21/36 = 1 19/36
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( 11+7)*2=18*2=36(см) - периметр прямоугольника