Найдите значение выражений

16)
$\frac{1}{ \frac{1}{3} + \frac{1}{7} } = \frac{1}{ \frac{7}{21} + \frac{3}{21} } = \frac{1}{ \frac{10}{21} } = \frac{21}{10} = 2.1$
17)
$\frac{1}{ \frac{1}{4} + \frac{1}{6} } = \frac{1}{ \frac{6}{24} + \frac{4}{24} } = \frac{1}{ \frac{10}{24} } = \frac{24}{10} = 2.4$
18)
$\frac{1}{ \frac{1}{8} + \frac{1}{12} } = \frac{1}{ \frac{3}{24} + \frac{2}{24} } = \frac{1}{ \frac{5}{24} } = \frac{24}{5} = \frac{48}{10} = 4.8$
19)
$\frac{1}{ \frac{1}{2} + \frac{1}{3} } = \frac{1}{ \frac{3}{6} + \frac{2}{6} } = \frac{1}{ \frac{5}{6} } = \frac{6}{5} = \frac{12}{10} = 1.2$