А)27/64 × 56/9 = 21/8 = 2 5/8
б)23/81 × 9 = 23/9 = 2 5/9
в)54/19 ÷ 2 = 54/19 × 1/2 = 27/19 = 1 8/19
г)16/45 ÷ 2/35 = 16/45 × 35/2 = 56/9 = 6 2/9
д)18/49 + 13/14 =(18 × 2 + 13 × 7)/98 = 36/98 + 91/98 = 127/98 = 1 29/98
е)15/39 + 4 = 5/13 + 4 =(5 ×1 + 4 ×13)/13 = 5/13 + 52/13 = 57/13 = 4 5/13
ж)21/2 - 8 = (21 × 1 - 8 × 2)/2 = 21/2 - 16/2 = 5/2 = 2 1/2
з)63/8 - 5/12 = (63 × 3 - 5 × 2)/24 = 189/24 - 10/24 = 179/24 = 7 11/24
и)1 4/7 ÷ 33/35 = 11/7 ÷ 33/35 = 11/7 × 35/33 = 5/3 = 1 2/3