1/6 + 5/8=4/24 + 15/24 = 19/24;
9/14 + 8/21 = 27/42 + 16/42 = 43/42 = 1 1/42;
0,2 +1/4 = 2/10 + 1/4 = 4/20 + 5/20 = 9/20 или 0,2 + 0,25 = 0,45.
5/6 - 3/4 = 10/12 - 9/12 = 1/12;
20/45 - 2/9=20/45 - 10/45 = 10/45 = 2/9;
7/9 + 5/12 - 3/4 = 28/36 + 15/36 + 27/36 = 70/36 = 1 34/36 = 1 17/18.