78. Найдите значение выражения: а) \(\frac49\cdot\frac{63}{64}\frac27\); б) \(\left(\frac12\right)^2:\frac56:\frac7{15}\); в) \(\left(1-\frac13\right):\left(\frac13-\frac14\right)\).

а)

\[\frac49\cdot\frac{63}{64}\cdot\frac27=\frac{4\cdot63\cdot2}{9\cdot64\cdot7}=\frac17.\]

б)

\[\left(\frac12\right)^2:\frac56:\frac7{15}=\frac14\cdot\frac65\cdot\frac{15}{7}=\frac{9}{14}.\]

в)

\[\left(1-\frac13\right):\left(\frac13-\frac14\right)=\frac23:\frac1{12}=\frac23\cdot12=8.\]

Ответ: а) \(\frac17\); б) \(\frac9{14}\); в) \(8\).