Bài 1 : Tính bằng cách hợp lí :
a ) A = \((\) \(\dfrac{\dfrac{1}{13}-\dfrac{1}{17}-\dfrac{1}{23}}{\dfrac{2}{13}-\dfrac{2}{17}-\dfrac{2}{23}}\) \()\) . \((\) \(\dfrac{\dfrac{1}{3}-0,25+0,2}{1\dfrac{1}{6}-0,875+0,7}\) \()\) + \(\dfrac{6}{7}\)
b ) B = 2000 : \([\) \((\) \(\dfrac{0,4-\dfrac{2}{9}+\dfrac{2}{11}}{1,4-\dfrac{7}{9}+\dfrac{7}{11}}\) \()\) . \((\) \(\dfrac{-1\dfrac{1}{6}+0,875-0,7}{\dfrac{1}{3}-0,25+\dfrac{1}{5}}\) \()\) \(]\)
c ) C = 10101 . \((\) \(\dfrac{5}{111111}+\dfrac{2}{222222}-\dfrac{4}{21.143.37}\) \()\)
Bài 2 : Tìm x :
a ) \(\dfrac{1}{2.5}+\dfrac{1}{5.8}+\dfrac{1}{8.11}+......+\dfrac{1}{125.155}-x=\dfrac{1}{310}\)
b ) \(1\dfrac{3}{5}+(\dfrac{\dfrac{2}{7}\dfrac{2}{17}\dfrac{2}{37}}{\dfrac{5}{7}\dfrac{5}{17}\dfrac{5}{37}}).\) x = \(\dfrac{16}{5}\)