D=I*c+r
3a:b=2 rest 5
3a=2b+5
2b/b+5/b=2 rest 5
2+(5/b)=2 rest 5
5/b=(c+r)/2
[tex] \frac{5}{b}= \frac{c+r}{y2} [/tex]
[tex]\frac{5}{b}= \frac{7}{2} [/tex]
b=[tex] \frac{5*2}{7} = \frac{10}{7} [/tex]
b=10/7
3a=2b+5
3a=20/7+5
21a=20+35
21a=55
a=55/21
daca faci verificarea
3a=2b+5
3*(55/21)=2*(10/7)+5 =>
55/7=20/7+5 aducem la acelasi numitor
55/7=20/7+7*5
55=20+35