\(\left(\dfrac{1}{68}+\dfrac{1}{968}-\dfrac{1}{1968}\right)\left(\dfrac{1}{23}-\dfrac{1}{6}-\dfrac{1}{6}\right)\)
\(=\dfrac{61657}{4048176}\cdot\left(-\dfrac{20}{69}\right)\)
\(=-\dfrac{61657}{1012044}\cdot\dfrac{5}{69}\)
\(=-\dfrac{308285}{69831036}\)
Tính nhanh
a) \(\dfrac{-3}{7}+\dfrac{15}{26}-\left(\dfrac{2}{13}-\dfrac{3}{7}\right)\)
b) \(2.\dfrac{3}{7}+\left(\dfrac{2}{9}-1\dfrac{3}{7}\right)-\dfrac{5}{3}:\dfrac{1}{9}\)
c) \(\dfrac{-11}{23}.\dfrac{6}{7}+\dfrac{8}{7}.\dfrac{-11}{23}-\dfrac{1}{23}\)
d) \(\left(\dfrac{377}{-231}-\dfrac{123}{89}+\dfrac{34}{791}\right).\left(\dfrac{1}{6}-\dfrac{1}{8}-\dfrac{1}{24}\right)\)
1.Tính nhanh:
e)\(\dfrac{\dfrac{1}{6}-\dfrac{1}{39}+\dfrac{1}{51}}{\dfrac{1}{8}-\dfrac{1}{12}+\dfrac{1}{68}}\)
f)\(\dfrac{7}{8}+\dfrac{7}{56}+\dfrac{7}{154}+...+\dfrac{7}{1400}\)
tìm x
\([\dfrac{6:\dfrac{3}{5}-1\dfrac{1}{16}.\dfrac{16}{7}}{4\dfrac{1}{5}-\dfrac{10}{11}+5\dfrac{2}{11}}-\dfrac{\left(\dfrac{3}{20}+\dfrac{1}{2}-\dfrac{1}{5}\right).\dfrac{12}{49}}{3\dfrac{1}{3}+\dfrac{2}{9}}].x=2\dfrac{23}{96}\)
(\(\dfrac{1}{5}-\dfrac{1}{6}-\dfrac{1}{30}\) ).(\(\dfrac{21}{22}+\dfrac{22}{23}+......+\dfrac{102}{103}\))
BT2: Tính nhanh
9) (\(\left(5+\dfrac{1}{5}-\dfrac{2}{9}\right)-\left(2-\dfrac{1}{23}-2\dfrac{3}{35}+\dfrac{5}{6}\right)-\left(8+\dfrac{2}{7}-\dfrac{1}{18}\right)\)
10)\(\dfrac{1}{3}-\dfrac{3}{4}-\left(-\dfrac{3}{5}\right)+\dfrac{1}{64}-\dfrac{2}{9}-\dfrac{1}{36}+\dfrac{1}{15}\)
Chứng tỏ rằng :
\(\dfrac{7}{12}\)<\(\dfrac{1}{21}+\dfrac{1}{22}+\dfrac{1}{23}+............+\dfrac{1}{40}\)<\(\dfrac{5}{6}\)
1 thực hiện phép tính
a,\(\dfrac{-2}{3}+\dfrac{3}{4}-\dfrac{-1}{6}+\dfrac{-2}{6}-\dfrac{-2}{5}\)
b,\(\dfrac{-2}{3}+\dfrac{-1}{5}+\dfrac{3}{4}-\dfrac{5}{6}-\dfrac{-7}{10}\)
c,\(\dfrac{1}{2}-\dfrac{-2}{5}+\dfrac{1}{3}+\dfrac{5}{7}-\dfrac{-1}{6}+\dfrac{-4}{35}+\dfrac{1}{41}\)
d,\(\dfrac{1}{100.99}-\dfrac{1}{99.98}-\dfrac{1}{98.97}-...-\dfrac{1}{3.2}-\dfrac{1}{2.1}\)
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 = \(\dfrac{16}{5}\)
1 Tính:
a)\(\dfrac{\dfrac{7}{10}+\dfrac{3}{5}}{\dfrac{7}{10}+\dfrac{1}{2}}\) b)\(\dfrac{6-\dfrac{1}{\dfrac{1}{2}-\dfrac{1}{3}}}{6+\dfrac{1}{\dfrac{1}{2}-\dfrac{1}{3}}}\)
