Câu hỏi của Trần Kim Cường

Question

Tìm x biết: $\dfrac{3x}{2.5}+\dfrac{3x}{5.8}+\dfrac{3x}{8.11}+\dfrac{3x}{11.14}=\dfrac{1}{21}$

Vu Thuy Linh · Accepted Answer

$x$ $($$\dfrac{3}{2.5}$ $+
$ $\dfrac{3}{5.8}$ $+$ $\dfrac{3}{8.11}$ $+$ $\dfrac{3}{11.14}$$)$ $=$ $\dfrac{1}{21}$$x$ $($$\dfrac{1}{2}$ $-$ $\dfrac{1}{5}$ $+$ $\dfrac{1}{5}$ $-$ $\dfrac{1}{8}$ $+$ $\dfrac{1}{8}$ $-$ $\dfrac{1}{11}$ $+$ $\dfrac{1}{11}$ $-$ $\dfrac{1}{14}$$)$ $=$ $\dfrac{1}{21}$$x$ $($$\dfrac{1}{2}$ $-$ $\dfrac{1}{14}$$)$ $=$ $\dfrac{1}{21}$$x$ x $\dfrac{3}{7}$ $=$ $\dfrac{1}{21}$$x$        $=$ $\dfrac{1}{21}$ $:$ $\dfrac{3}{7}$ $x$        $=$ $\dfrac{1}{9}$ Câu trả lời: $x$ $($$\dfrac{3}{2.5}$ $+
$ $\dfrac{3}{5.8}$ $+$ $\dfrac{3}{8.11}$ $+$ $\dfrac{3}{11.14}$$)$ $=$ $\dfrac{1}{21}$$x$ $($$\dfrac{1}{2}$ $-$ $\dfrac{1}{5}$ $+$ $\dfrac{1}{5}$ $-$ $\dfrac{1}{8}$ $+$ $\dfrac{1}{8}$ $-$ $\dfrac{1}{11}$ $+$ $\dfrac{1}{11}$ $-$ $\dfrac{1}{14}$$)$ $=$ $\dfrac{1}{21}$$x$ $($$\dfrac{1}{2}$ $-$ $\dfrac{1}{14}$$)$ $=$ $\dfrac{1}{21}$$x$ x $\dfrac{3}{7}$ $=$ $\dfrac{1}{21}$$x$        $=$ $\dfrac{1}{21}$ $:$ $\dfrac{3}{7}$ $x$        $=$ $\dfrac{1}{9}$

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