1. 1/2+5/6-7/9=(1*9+3*5-2*7)/18=(9+15-14)/18=10/18=5/9;
2. ⁵/₉:1²/₃=⁵/₉:⁵/₃=(5*3)/(9*5)=3/9=1/3;
3. 15:2,4=6,25=6¹/₄=25/4;
4. (25/4)-6¹/₃₆=(25/4)-(217/36)=(25*9-1*217)/36=(225-217)/36=8/36=2/9;
5. (1/3):(2/9)=(1*9)/(3*2)=3/2=1,5;
6. 2,75-3-2/3=2³/₄-2/3=(11/4)-(2/3)=(3*11-2*4)/12=(33-8)/12=25/12;
7. (25/12)*1,2=(25/12)*1¹/₅=(25/12)*(6/5)=5/2=2,5;
8. (7/30)+(5/12)=(7*2+5*5)/60=(14+25)/60=39/60=13/20;
9. (13/20):(13/100)=13*100/(13*20)=5;
10. 2,5:5=0,5;
11. 1,5+0,5=2;
12. 2:0,125=2:(1/8)=2*8=16.
Ответ: А.