Răspuns:
Explicație pas cu pas:
3)a)[tex]\frac{a}{b}=\frac{7}{8} ;a=\frac{7b}{8} \\ \frac{2a}{5b}=\frac{7b}{4}*\frac{1}{5b}=\frac{7}{20}[/tex]
b)[tex]\frac{3a+b}{2b-a} =\frac{\frac{21b}{8}+b }{2b-\frac{7b}{8} } =\frac{29}{9}[/tex]
c)daca a+b=30 si a=7b/8
obtinem
7b/8+b=30
7b+8b=240
15b=240
b=16 si a=30-16=14
