Răspuns:
[tex]a=\frac{1}{2}+\frac{1}{3}+\frac{1}{4}=\frac{6+4+3}{12}=\frac{13}{12}\\b=\frac{1}{2}+\frac{2}{3}+\frac{3}{4}=\frac{6}{12}+\frac{8}{12}+\frac{9}{12}=\frac{23}{12}\\a+b=\frac{13}{12}+\frac{23}{12}=\frac{36}{12}=3[/tex]
Explicație pas cu pas: