notam nr cu a,b,c
a+b+c=450
[tex]a = 20\%450 = \frac{20}{100} \times 450 = \\ \frac{1}{5} \times 450 = \frac{450}{5} = 90[/tex]
[tex]b = \frac{8}{9} \times a = \frac{8a}{9} = \frac{8 \times 90}{9} = \\ \frac{720}{9} = 80[/tex]
a+b+c=450
90+80+c=450
170+c=450
c=450-170
c=280
