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$f, \dfrac{\bigg(0,34-\dfrac1{25}\bigg)÷\dfrac52}{0,8÷\bigg(\dfrac45·1,25\bigg)}-(1,2·0,35)÷\dfrac{-4}5$
$=\dfrac{\dfrac3{10}÷\dfrac52}{\dfrac45÷1}-\dfrac{21}{50}÷\dfrac{-4}5$
$=\dfrac{\dfrac3{25}}{\dfrac45}+\dfrac{21}{40}$
$=\dfrac{3}{20}+\dfrac{21}{40}$
$= \dfrac6{40}+\dfrac{21}{40}$
$= \dfrac{27}{40}$