3:4 1/5+5,4:7,2-2/7:0,8=

3 : 4 1/5 + 5,4 : 7,2 - 2/7 : 0,8 = 1 3/28

1) 3 : 4 1/5 = 3 : 21/5 = 3 × 5/21 = 5/7

2) 5,4 : 7,2 = 0,75 = 3/4

3) 2/7 : 0,8 = 2/7 : 4/5 = 2/7 × 5/4 = 1/7 × 5/2 = 5/14

4) 5/7 + 3/4 = 20+21/28 = 41/28 = 1 13/28

5)1 13/28 - 5/14 = 1 13-10/28 = 1 3/28