la ex.1 si 3 ti-am raspuns la o alta postare
2) 2x-20x/100=27
2x-x/5=27
(5·2x-x)/5=27
10x-x=27·5
9x=135
x=135/9
x=15
4) x/4-3,5=3x/5
x/4-35/10=3x/5 simplificam 35/10 cu 5
x/4-7/2=3x/5
(x-7·2)/2=3x/5
(x-14)/4=3x/5
5(x-14)=4·3x
5x-70=12x
5x-12x=70
-7x=70 inmultim -1
7x=-70
x=-70/7
x=-10