Вычислите: 1) 4/7 + 2/5; 2) 7/12 - 5/9; 3) 2 3/4 + 3 2/5; 4) 3 4/9 - 2 1/6.

1) 4/7  +  2/5  = 20/35  +  14/35  = 34/35 2) 7/12 - 5/9 = 21/36 - 20/36 = -1/36 3) 2 3/4 + 3 2/5 = 2  +  3 + ( 3/4 + 2/5  ) = 5 + ( 15/20 + 8/20  ) = 6 3/20 4) 3 4/9 - 2 1/6 = 31/9 - 13/6 = 62/18 - 39/18 = 23/18= 1 5/18