1) 11/50 - 3/25 = 11/50 - 6/50 = 5/50 = 1/10
1/10 + 1/20 = 2/20 + 1/20 = 3/20
2) 11/15 - 3/10 = 22/30 - 9/30 = 13/30
13/30 + 1/45 = 39/90 + 2/90 = 41/90
3) 7 - 2 4/11 = 4 7/11
1 5/17 х 4 7/11 = 22/17 х 51/11 = 22 х 3/11 = 66/11 = 6
4) 3 7/15 + 8 9/20 = 52/15 + 169/20 = 208/60 + 507/60 = 715/60 = 11 11/12
143/12 : 11/20 = 143/12 х 20/11 = 13/12 х 20 = 260/12 = 21 2/3