№507.
1) 2.8х-0.6+4.2х+16.8-7х=2.8х+4.2х-7х-0.6+16.8=16.2;
2)13.5у+7-5.2+8.9у-22.4=13.5у+8.9у+7-5.2-22.4=22.4у-20.6;
3)1.5х-1.8+3.1х-2.9+1.6х=1.5х+3.1х+1.6х-1.8-2.9=6.2х-4.7;
4)5у-у+0.8+1.6-3у-у=5у-у-3у-у+0.8+1.6=2.4.
№506.
1)-13.7-(-х)=-4.9; 2)6.1-(-у)=-5.2; 3)-2.9+(-х)=-3.8; 4)х+(-0.35)=2.3; 5)-23.5+(-у)=-4.6;
-13.7+х=-4.9: 6.1+у=-5.2; -2.9-х=-3.8; х-0.35=2.3; -23.5-у=-4.6;
х=8.8. у=-11.3. х=-0.9. х=2.65. у=-18.9.
6)у+(-48.3)=-78.5;
у-48.3=-78.5;
у=-30.2.