найдите значения выражений 1/ 1/30 + 1/42

 \frac{1}{ \frac{1}{30} + \frac{1}{42} } = \frac{1}{\frac{1}{5*6} + \frac{1}{6*7}}  = \frac{1}{\frac{7 + 5}{5*6*7}} = \frac{1}{\frac{12}{5*6*7}} = \frac{1}{\frac{2}{5*7}} = \frac{1}{\frac{2}{35}} = \frac{35}{2}