問題
$0.7\times 1\dfrac{3}{7}-1.4\times\bigg(3.75-\dfrac{5}{7}\bigg)\div\dfrac{17}{3}=\square$
解説
$0.7=\dfrac{7}{10},\ 1\dfrac{3}{7}=\dfrac{10}{7}$より, $0.7\times 1\dfrac{3}{7}=\dfrac{7}{10}\times\dfrac{10}{7}=1$
また, $3.75=\dfrac{15}{4}$なので, $3.75-\dfrac{5}{7}=\dfrac{15}{4}-\dfrac{5}{7}=\dfrac{105-20}{28}=\dfrac{85}{28}$
さらに, $1.4=\dfrac{7}{5}$より,
$1.4\times\bigg(3.75-\dfrac{5}{7}\bigg)\div\dfrac{17}{3}
=\dfrac{7}{5}\times\dfrac{85}{28}\times\dfrac{3}{17}=\dfrac{119}{28}\times\dfrac{3}{17}
=\dfrac{7}{28}\times 3
=\dfrac{3}{4}$
よって, $1-\dfrac{3}{4}=\dfrac{1}{4}$
従って, $\square=$$\dfrac{1}{4}$となります.
