решение по действиям
1)3,9-2,55 = 1,35
2) 1,35 + 4 5/12 = 1 35/100 + 53/12 = 1 7/20 + 53/12 = 27/20 + 53/12 = 81+265/60 = 346/60
3) 346/60 - 1 1/15 = 346/60 - 16/15 = 346/60 - 64/60 = 282/60
4) 282/60 : 4,7 = 282/60 : 4 7/10 = 282/60 : 47/10 = 282*10/60*47 = 6/6 = 1
5) 0,81 * 8 1/3 = 81/100 * 25/3 = 81*25/100*3 = 27/4
6) 0,57 : 4 3/4 = 57/100 : 19/4 = 57*4/100*19 = 3/25
7) 27/4 - 3/25 = 675/100 - 12/100 =663/100
8) 663/100 : 2,21 = 663/100 : 2 21/100 = 663/100 : 221/100 = 663*100/100*221 = 3
9) 4,125 : 2 1/6 = 4 125/1000 : 13/6 = 4 1/8 : 13/6 = 33/8 : 13/6 = 33*6/8*13 = 99/52
10) 3 + 99/52 = 2 52/52 + 99/52 = 156/52 + 99/52 = 255/52
11) 1: 255/52= 52/52 : 255/52 = 52*52/52*255 = 52/255