a)\(\dfrac{3}{5}x\dfrac{20}{18}:\dfrac{2}{9}-\dfrac{1}{5}\)
=\(\dfrac{2}{3}:\dfrac{1}{45}\)
=30
b)\(\dfrac{2}{5}+\dfrac{6}{7}x\dfrac{7}{15}\)
=\(\dfrac{2}{5}+\dfrac{2}{5}\)=\(\dfrac{4}{5}\)
c)\(\left(\dfrac{5}{2}+\dfrac{1}{8}\right):\left(1-\dfrac{7}{6}\right)\)
=\(\left(\dfrac{20}{8}+\dfrac{1}{8}\right):\dfrac{-1}{6}\)
=\(\dfrac{21}{8}:\dfrac{-1}{6}\)=-15\(\dfrac{3}{4}\)
a, 3/5 x 20/18 : 2/9 - 1/15.
=\(\dfrac{3x20}{5x18}x\dfrac{2}{9}-\dfrac{1}{15}=\dfrac{3x20x2}{5x18x9}-\dfrac{1}{15}=\dfrac{3x5x4x2}{5x2x9x3x3}-\dfrac{1}{15}\)
\(=\dfrac{4}{9x3}-\dfrac{1}{15}=\dfrac{4}{27}-\dfrac{1}{15}=\dfrac{20}{135}-\dfrac{9}{135}=\dfrac{11}{135}\)
b, 2/5 + 6/7 x 7/15.
\(=\dfrac{2x6x7}{5x7x15}=\dfrac{2x2x3x7}{5x7x3x5}=\dfrac{2x2}{5x5}=\dfrac{4}{25}\)
c, (5/2 + 1/8) : ( 1 - 7/6 ).
=\(\left(\dfrac{20}{8}+\dfrac{1}{8}\right):\left(\dfrac{6}{6}-\dfrac{7}{6}\right)=\dfrac{21}{8}:-\dfrac{1}{6}=\dfrac{21}{8}x\dfrac{-6}{1}\)
\(=\dfrac{31x\left(-6\right)}{8x1}=-\dfrac{186}{8}=-\dfrac{39}{4}\)
bài 2 : thực hiện phép tính
\(a,\dfrac{3}{5}\times\dfrac{20}{18}:\dfrac{2}{9}-\dfrac{1}{15}=\left(\dfrac{3}{5}\times\dfrac{20}{18}:\dfrac{2}{9}\right)-\dfrac{1}{15}=\left(\dfrac{3}{5}\times\dfrac{20}{18}\times\dfrac{9}{2}\right)-\dfrac{1}{15}=\left(\dfrac{3\times20\times9}{5\times18\times2}\right)-\dfrac{1}{15}=\dfrac{540}{180}-\dfrac{1}{15}=3-\dfrac{1}{15}=\dfrac{3}{1}-\dfrac{1}{15}=\dfrac{3\times15}{1\times15}-\dfrac{1}{15}=\dfrac{45}{15}-\dfrac{1}{15}=\dfrac{45-1}{15}=\dfrac{44}{15}\)
\(b,\dfrac{2}{5}+\dfrac{6}{7}\times\dfrac{7}{15}=\dfrac{2}{5}+\left(\dfrac{6}{7}\times\dfrac{7}{15}\right)=\dfrac{2}{5}+\left(\dfrac{6\times7}{7\times15}\right)=\dfrac{2}{5}+\dfrac{42}{105}=\dfrac{2}{5}+\dfrac{2}{5}=\dfrac{2+2}{5}=\dfrac{4}{5}\)
\(c,\left(\dfrac{5}{2}+\dfrac{1}{8}\right):\left(1-\dfrac{7}{6}\right)=\left(\dfrac{5\times4}{2\times4}+\dfrac{1}{8}\right):\left(\dfrac{1}{1}-\dfrac{7}{6}\right)=\left(\dfrac{20}{8}+\dfrac{1}{8}\right):\left(\dfrac{1\times6}{1\times6}-\dfrac{7}{6}\right)=\left(\dfrac{20+1}{8}\right):\left(\dfrac{6}{6}-\dfrac{7}{6}\right)=\dfrac{21}{8}:\left(\dfrac{6-7}{6}\right)=\dfrac{21}{8}:-\dfrac{1}{6}=\dfrac{21}{8}\times-\dfrac{6}{1}=\dfrac{21\times\left(-6\right)}{8\times1}=-\dfrac{126}{8}=-\dfrac{63}{4}.\)
