Вычислите: а)1/4+4/7+9/28 б)1/5+3/10+7/20 в)3/20+7/30+2/40 г)17/20+23/30+11/60 д)...

A) $\frac{1}{4} + \frac{4}{7} + \frac{9}{28} = \frac{7+16+9}{28}$ = $\frac{32}{28} =1 \frac{4}{28} = 1 \frac{1}{7}$
б) $\frac{1}{5} + \frac{3}{10} + \frac{7}{20} = \frac{4+6+7}{20} = \frac{17}{20}$
в) $\frac{3}{20} + \frac{7}{30} + \frac{2}{40} = \frac{18 + 28 + 6}{120} = \frac{52}{120}$
г) $\frac{17}{20} + \frac{23}{30} + \frac{11}{60} = \frac{51 + 46 + 11}{60} = \frac{108}{60} = 1 \frac{48}{60} = 1 \frac{16}{20}$
д) 3/20 + 7/30 + 9/50 = 169/300
е) $\frac{7}{40} + \frac{11}{70} + \frac{13}{30} = \frac{147 + 132 + 364 }{840} = \frac{643}{840}$ (но, возможо, неправильно)