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Question

Tìm x:

($\frac{1}{12}+\frac{1}{20}+\frac{1}{30}+....+\frac{1}{90}$) .x = $\frac{14}{30}$

Pisces · Accepted Answer

$\left(\frac{1}{12}+\frac{1}{20}+\frac{1}{30}+...+\frac{1}{90}\right).x=\frac{14}{30}$

$\left(\frac{1}{3.4}+\frac{1}{4.5}+\frac{1}{5.6}+...+\frac{1}{9.10}\right).x=\frac{14}{30}$

$\left(\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+...+\frac{1}{9}-\frac{1}{10}\right).x=\frac{14}{30}$

$\left(\frac{1}{3}-\frac{1}{10}\right).x=\frac{14}{30}$

$\frac{10-3}{30}.x=\frac{14}{30}$

$\frac{7}{30}.x=\frac{14}{30}$

$x=\frac{14}{30}:\frac{7}{30}$

$x=\frac{14}{30}.\frac{30}{7}$

$x=2$Câu trả lời: $\left(\frac{1}{12}+\frac{1}{20}+\frac{1}{30}+...+\frac{1}{90}\right).x=\frac{14}{30}$