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Решите задачу:

$\frac{1}{ \frac{1}{36}+ \frac{1}{45} } = \frac{1}{ \frac{5+4}{180}} = \frac{1}{ \frac{9}{180}} = \frac{1}{ \frac{1}{20} } = 1 * \frac{20}{1} = 20 \\ \frac{1}{ \frac{1}{63} + \frac{1}{72}} = \frac{1}{ \frac{8+7}{504} } = \frac{1}{ \frac{15}{504} } = \frac{1}{ \frac{5}{168} } = 1 * \frac{168}{5} = \frac{168}{5} = 33.6 \\$
$\frac{1}{ \frac{1}{30}+ \frac{1}{45} } = \frac{1}{ \frac{7+5}{210} } = \frac{1}{ \frac{12}{210}} = \frac{1}{ \frac{2}{35} } = 1* \frac{35}{2} = \frac{35}{2} = 17.5$