Fie a, b, c cele trei numere.
[tex]\displaystyle\frac{a+b}{2}=9.1\Rightarrow a+b=2\cdot9.1=18.2\\\\\displaystyle\frac{b+c}{2}=19.8\Rightarrow b+c=2\cdot 19.8=39.6\\\\\displaystyle\frac{a+c}{2}=13.4\Rightarrow a+c=2\cdot13.4=26.8[/tex]
Adunam toate cele trei ecuatii si obtinem:
[tex](a+b)+(b+c)+(a+c)=18.2+39.6+26.8\\2a+2b+2c=84.6\\2(a+b+c)=84.6\\a+b+c=\displaystyle\frac{84.6}{2}=42.3[/tex]
Deci [tex]a+b+c=42.3[/tex]. Cum [tex]a+b=18.2[/tex], avem ca [tex]18.2+c=42.3\\c=42.3-18.2=24.1\\\\a+c=26.8\Rightarrow a+24.1=26.8\Rightarrow a=26.8-24.1=2.7\\\\b+c=39.6\Rightarrow b+24.1=39.6\Rightarrow b=39.6-24.1=15.5[/tex]
