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\(\dfrac{3}{8}+\dfrac{1}{4}=\dfrac{3}{8}+\dfrac{2}{8}=\dfrac{5}{8}\)
=> Chọn A
a) \(\left(8\frac{4}{5}x-50\right):0,4=5\)
\(\Rightarrow\left(\frac{44}{5}x-50\right)=5.0,4\)
\(\Rightarrow\frac{44}{5}x-50=2\)
\(\Rightarrow\frac{44}{5}x=2+50\)
\(\Rightarrow\frac{44}{5}x=52\)
\(\Rightarrow x=\frac{65}{11}\)
b) \(\left(\frac{5x}{3}-3\right):15=\frac{3}{10}\)
\(\Rightarrow\frac{5x}{3}-3=\frac{3}{10}.15\)
\(\Rightarrow\frac{5x}{3}-3=\frac{45}{10}\)
\(\Rightarrow\frac{5x}{3}=\frac{45}{10}+3\)
\(\Rightarrow\frac{5x}{3}=\frac{15}{2}\)
\(\Rightarrow5x.2=3.15\)
=> 5x.2 = 45
=> 5x = 45 : 2
=> 5x = 45/2
=> x = 9/2
viết rõ lại cái đề giùm tui tui mới làm được
\(a.32,5-3\cdot0,87=32,5-2,61=29,89\)
\(8,5\cdot\left(1\dfrac{1}{2}+\dfrac{4}{4}\right):5=8,5\cdot\left(\dfrac{3}{2}+\dfrac{4}{4}\right):5\\ =8,5\cdot\left(\dfrac{6}{4}+\dfrac{4}{4}\right):5\\ =8,5\cdot\dfrac{10}{4}:5\\ =\dfrac{85}{4}:5\\ =\dfrac{17}{4}\)
\(b.30,96-6,45+14,4:3=30,96-6,45+4,8\\ =29,31\)
\(\dfrac{2}{5}\cdot\left(\dfrac{4}{5}-\dfrac{1}{2}\right)=\dfrac{2}{5}\cdot\left(\dfrac{8}{10}-\dfrac{5}{10}\right)\\ =\dfrac{2}{5}\cdot\dfrac{3}{10}=\dfrac{3}{25}\)
bài 2
\(a.2,5\cdot12,5\cdot8\cdot0,4=\left(2,5\cdot0,4\right)\left(12,5\cdot8\right)\\ =1\cdot100=100\)
b,\(\dfrac{12}{15}\cdot\dfrac{5}{6}\cdot\dfrac{3}{20}\cdot\dfrac{32}{5}=\dfrac{12\cdot5\cdot3\cdot32}{15\cdot6\cdot20\cdot5}\\ =\dfrac{3\cdot4\cdot5\cdot3\cdot4\cdot8}{3\cdot5\cdot2\cdot3\cdot5\cdot4\cdot5}=\dfrac{16}{25}\)
Bài 1:
a) \(32.5-3\cdot0.87=32.5-2.61=29.89\)
\(8.5\cdot\left(1\dfrac{1}{2}+\dfrac{4}{4}\right):5=8.5\cdot\dfrac{5}{2}:5=\dfrac{17}{2}\cdot\dfrac{5}{2}:5=\dfrac{85}{4}\cdot\dfrac{1}{5}=\dfrac{17}{4}\)