Giải bài 60 trang 31 - Sách giáo khoa Toán 7 tập 1

Đề bài

Hướng dẫn giải

a) \(\dfrac{1}{3}x : \dfrac{2}{3}= 1\dfrac{3}{4} :\dfrac{2}{5} \Rightarrow \dfrac{x}{3}:\dfrac{2}{3} = \dfrac{7}{4}:\dfrac{2}{5} \Rightarrow \dfrac{x}{3} = \dfrac{\dfrac{7}{4}.\dfrac{2}{3}}{\dfrac{2}{5}} \Rightarrow \dfrac{x}{3} = \dfrac{7}{6}.\dfrac{5}{2}\)

\(\Rightarrow \dfrac{x}{3} = \dfrac{35}{12} \Rightarrow x = \dfrac{35.3}{12} \Rightarrow x = \dfrac{35}{4} = 8\dfrac{3}{4}\)

b) 4,5 : 0,3 = 2,25 : (0,1.x) \(\Rightarrow\) 0,1.x = \(\dfrac{2,25.0,3}{4,5}\)

\(\Rightarrow\) 0,1.x = 0,15 \(\Rightarrow\) x = 1,5

c) 8 : \((\dfrac{1}{4}.x)\) = 2 : 0,02 \(\Rightarrow\) \(\dfrac{x}{4} = \dfrac{8.0,02}{2} \Rightarrow \dfrac{x}{4} = 0,08\)

\(\Rightarrow\) x = 0,08.4 \(\Rightarrow\) x = 0,32

d) 3 : 2 \(\dfrac{1}{4}\) = \(\dfrac{3}{4}\) : (6.x) \(\Rightarrow\) 3 : \(\dfrac{9}{4} = \dfrac{3}{4}\) : (6.x) \(\Rightarrow\) 6.x = \(\dfrac{ \dfrac{3}{4}.\dfrac{9}{4}}{3}\)

\(\Rightarrow\) 6.x = \(\dfrac{27}{16}.\dfrac{1}{3}\) \(\Rightarrow\) 6.x = \(\dfrac{9}{16}\) \(\Rightarrow\) x = \(\dfrac{9}{16}\) : 6 \(\Rightarrow\) x = \(\dfrac{3}{32}\)