a) [tex]0,a+0,b+0,c=0,7 <=> \frac{a}{10}+ \frac{b}{10}+ \frac{c}{10}= \frac{7}{10} [/tex]. Inmultim cu 10, si obtinem: [tex]a+b+c=7[/tex].
b) [tex]a,b+b,c+c,a=7,7 <=> \frac{ab}{10}+ \frac{bc}{10}+ \frac{ca}{10} = \frac{77}{10} [/tex]. Inmultim cu 10, si obtinem: [tex]a+b+c=77[/tex].
c)[tex]0,ab+0,bc+0,ca=0,77 <=. \frac{ab}{100}+ \frac{bc}{100}+ \frac{ca}{100}= \frac{77}{100} [/tex]. Inmultim cu 100, si obtinem: [tex]a+b+c=77[/tex].