Решение

1) 3 2/3 + 1 3/4 = 11/3 + 7/4 = 4•11+3•7/12 = 65/12 = 5 5/12

2) 6 7/12 - 2 1/4 = 79/12 - 9/4 = 79-3•9/12= 52/12 = 13•4/3•4 = 4 1/3

3) 5 5/12 :4 1/3= 65/12:13/3 = 65•3/12•13 = 195/156 = 5•39/4•39 (39 сокращаем на1) = 5/4 = 1 1/4