19
13/50-1/20=26/100-5/100=21/100
21/100*3 4/7=21/100*25/7=3/4
5/12*1 7/15=5/12*22/15=11/18
3/4+11/18=27/36+22/36=49/36=1 13/36
16
-3 1/7*(-8)=-22/7*(-8)=176/7=25 1/7
2,9:0,1=29
11/21:(-3 2/3)=11/21:(-11/3)=11/21*(-3/11)=-1/7
25 1/7-29+(-1/7)=25 1/7+(-29-1/7)=25 1/7-29 1/7=-4