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![](https://rs.olm.vn/images/avt/0.png?1311)
\(B=\frac{10}{18}\times\frac{22}{30}\times\frac{36}{44}\times...\times\frac{200}{209}=\frac{1\times10}{2\times9}\times\frac{2\times11}{3\times10}\times\frac{3\times12}{4\times11}\times...\times\frac{10\times20}{11\times19}\)
\(=\frac{1\times10\times2\times11\times3\times12\times...\times10\times20}{2\times9\times3\times10\times4\times11\times...\times11\times19}=\frac{\left(1\times2\times3\times...\times10\right)\times\left(10\times11\times12\times...\times20\right)}{\left(2\times3\times4\times...\times11\right)\times\left(9\times10\times11\times...\times19\right)}\)
\(=\frac{1\times20}{11\times9}=\frac{20}{99}\)
Sửa đề \(C=\left(1-\frac{1}{4}\right)\times\left(1-\frac{1}{9}\right)\times\left(1-\frac{1}{16}\right)\times...\times\left(1-\frac{1}{100}\right)\)
\(=\frac{3}{4}\times\frac{8}{9}\times\frac{15}{16}\times...\times\frac{99}{100}=\frac{3\times8\times15\times...\times99}{4\times9\times16\times...\times100}=\frac{1\times3\times2\times4\times3\times5\times...\times9\times11}{2\times2\times3\times3\times4\times4\times...\times10\times10}\)
\(=\frac{\left(1\times2\times3\times....\times9\right)\times\left(3\times4\times5\times...\times11\right)}{\left(2\times3\times4\times...\times10\right)\times\left(2\times3\times4\times...\times10\right)}=\frac{1\times11}{10\times2}=\frac{11}{20}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(x+x\times\dfrac{1}{4}+x\times\dfrac{3}{4}=200\)
\(x\times\left(1+\dfrac{1}{4}+\dfrac{3}{4}\right)=200\)
\(x\times\left(1+1\right)=200\)
\(x\times2=200\)
\(x=200:2\)
\(x=100\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(460+85x4=\left(y+200\right):4\)
\(460+340=\left(y+200\right):4\)
\(800=\left(y+200\right):4\)
\(y+200=800x4\)
\(y+200=3200\)
\(y=3200-200\)
\(y=3000\)
460 + 85 × 4 = y + 200/4
460 + 340 = y + 50
y + 50 = 800
y = 800 - 50
y = 750
170
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mình
nhé
200 x 4 : 4 - 30
= 200 - 30
= 170