7/15-3/40-1/24=56/120-9/120-5/120=42/120=7/20
7/20:0,7=7/20:7/10=7/20*10/7=1/2
2,4*1/3=24/10*1/3=8/10=0,8
0,8-3=-2,2
-2,2*5/11=-22/10*5/11=-2/2=-1
1/2:(-1)=-1/2
3/4-1 2/3=9/12-20/12=-11/12
1 5/6:(-11/12)=11/6:(-11/12)=11/6*(-12/11)=-2
4/9-5/12+75/100=4/9-5/12+3/4=16/36-15/36+27/36=28/36=7/9
7/9*3/7=1/3
-2:1/3=-2*3/1=-6
-1/2*(-6)=3