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Dế thấy \(0,\overline{xy}< 1\Rightarrow19.94+0,\overline{xy}< 20,94\)
\(\Rightarrow\overline{xy},\overline{mn}< 20,94\Rightarrow\overline{xy}\le20\)
Mà\(19,94< \overline{xy},\overline{mn}\Rightarrow\overline{xy}\ge19\)
\(\Rightarrow\overline{xy}=19;\overline{xy}=20\)
Nếu \(\overline{xy}=19\Rightarrow19,\overline{mn}=19,94+0,19=20,13\left(L\right)\)
Nếu \(\overline{xy}=20\Rightarrow20,\overline{mn}=19,94+0,20=20,14\Rightarrow\overline{mn}=14\)
Vậy ta có phép tính sau: 20,14=19,94+0,20
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A = \(\frac{1}{2}+\frac{5}{6}+\frac{11}{12}+......+\frac{109}{110}\)
A = \(1-\frac{1}{2}+1-\frac{1}{6}+1-\frac{1}{12}....+1-\frac{1}{110}\)
A = \(10-\left(\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+....+\frac{1}{110}\right)\)
A = \(10-\left(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+....+\frac{1}{10}-\frac{1}{11}\right)\)
A = \(10-\left(1-\frac{1}{11}\right)\)
A = \(10-\frac{10}{11}\)
A = \(\frac{100}{11}\)
xy=20
mn=14