7) x,y dp 5,7 2x-y=30 ; x/5=y/7=k => x=5k si y=7k ;inlocuiesti in 2x-y=30; 2x=2×5k=10k si y=7k => 10k-7k=30 => 3k =30 => k=10=> x=5k=10×5=50 si y=7k=10×7=70
8) x,y ip 0,(3) si 0,25 x×y=300
=>x×0,(3)=y×o,25=k=> x=k/0,(3); y=k/0,25 si x×y=300=> k/0,(3)× k/0,25=300
