1) 4:20/23=4*23/20= сократим 4 и 20 на 4=23/5=4 3/5
2) 2/7-4 11/14=-(4 11/14-4/14)=-4 7/14=-4 1/2
3) 2 4/15*(-4 1/2)=-34/15*9/2=-(34*9)/(15*2)= сократим 9 и 15 на 3; 34 и 2 на 2=
-(17*3)/5=-51/5=-10 1/5
4) 4 3/5-10 1/5=-(10 1/5-4 3/5)=-(6 1/5-3/5)=-(5 6/5-3/5)=-5 3/5.