903. Ҷамъи касрҳоро иҷро карда, натиҷаро (имкон дошта бошад) сода намоед: а) \(\frac{12}{21}+\frac{15}{42}\); б) \(\frac{7}{5}+\frac{11}{18}\); в) \(\frac{156}{169}+\frac{1}{13}\); г) \(\frac{5}{19}+\frac{13}{29}\).

а) \(\frac{12}{21}+\frac{15}{42}=\frac{24}{42}+\frac{15}{42}=\frac{39}{42}=\frac{13}{14}.\)

б) \(\frac{7}{5}+\frac{11}{18}=\frac{126}{90}+\frac{55}{90}=\frac{181}{90}=2\frac{1}{90}.\)

в) \(\frac{156}{169}+\frac{1}{13}=\frac{156}{169}+\frac{13}{169}=1.\)

г) \(\frac{5}{19}+\frac{13}{29}=\frac{145}{551}+\frac{247}{551}=\frac{392}{551}.\)