Tính rồi rút gọn.
a) \(\dfrac{5}{11}\times\dfrac{11}{6}\) b) \(7\times\dfrac{6}{21}\)
Tính bằng cách thuận tiện.
a) \(\dfrac{3}{5}\times\dfrac{17}{21}+\dfrac{2}{5}\times\dfrac{17}{21}\) b) \(\dfrac{11}{19}\times\dfrac{2}{7}+\dfrac{5}{7}\times\dfrac{11}{19}\)
a) \(\dfrac{3}{5}\times\dfrac{17}{21}+\dfrac{2}{5}\times\dfrac{17}{21}\)
\(=\dfrac{17}{21}\times\left(\dfrac{3}{5}+\dfrac{2}{5}\right)\)
\(=\dfrac{17}{21}\times1\)
\(=\dfrac{17}{21}\)
b) \(\dfrac{11}{19}\times\dfrac{2}{7}+\dfrac{5}{7}\times\dfrac{11}{19}\)
\(=\dfrac{11}{19}\times\left(\dfrac{2}{7}+\dfrac{5}{7}\right)\)
\(=\dfrac{11}{19}\times1\)
\(=\dfrac{11}{19}\)
a: =17/21(3/5+2/5)
=17/21*5/5
=17/21
b: =11/19(2/7+5/7)
=11/19*1
=11/19
Tính rồi rút gọn.
a) \(\dfrac{3}{8}:\dfrac{9}{4}\) b) \(\dfrac{8}{21}:\dfrac{4}{7}\) c) \(\dfrac{5}{8}:\dfrac{15}{8}\)
a) \(\dfrac{3}{8}:\dfrac{9}{4}\)
\(=\dfrac{3}{8}\times\dfrac{4}{9}\)
\(=\dfrac{3\times4}{8\times9}\)
\(=\dfrac{1\times1}{2\times3}\)
\(=\dfrac{1}{6}\)
b) \(\dfrac{8}{21}:\dfrac{4}{7}\)
\(=\dfrac{8}{21}\times\dfrac{7}{4}\)
\(=\dfrac{8\times7}{21\times4}\)
\(=\dfrac{2\times1}{3\times1}\)
\(=\dfrac{2}{3}\)
c) \(\dfrac{5}{8}:\dfrac{15}{8}\)
\(=\dfrac{5}{8}\times\dfrac{8}{15}\)
\(=\dfrac{5\times8}{8\times15}\)
\(=\dfrac{1\times1}{1\times3}\)
\(=\dfrac{1}{3}\)
a: \(=\dfrac{3}{8}\cdot\dfrac{4}{9}=\dfrac{12}{72}=\dfrac{1}{6}\)
b: \(=\dfrac{8}{21}\cdot\dfrac{7}{4}=\dfrac{56}{84}=\dfrac{2}{3}\)
c: \(=\dfrac{5}{8}\cdot\dfrac{8}{15}=\dfrac{5}{15}=\dfrac{1}{3}\)
Tính rồi rút gọn:
a) \(\dfrac{2}{9}+\dfrac{1}{9}\) b) \(\dfrac{5}{6}+\dfrac{1}{6}\) c) \(\dfrac{11}{8}-\dfrac{5}{8}\) d) \(\dfrac{5}{21}-\dfrac{2}{21}\)
Tìm phân số thích hợp.
a) \(?:\dfrac{2}{7}=\dfrac{5}{11}\) b) \(\dfrac{3}{4}:?=\dfrac{5}{8}\) c) \(?\times\dfrac{6}{11}=1\)
\(a,?=\dfrac{5}{11}\times\dfrac{2}{7}=\dfrac{10}{77}\\ b,?=\dfrac{3}{4}:\dfrac{5}{8}=\dfrac{3}{4}\times\dfrac{8}{5}=\dfrac{6}{5}\\ c,?=1:\dfrac{6}{11}=\dfrac{11}{6}\)
a) \(?:\dfrac{2}{7}=\dfrac{5}{11}\)
\(?=\dfrac{5}{11}\times\dfrac{2}{7}\)
\(?=\dfrac{10}{77}\)
b) \(\dfrac{3}{4}:?=\dfrac{5}{8}\)
\(?=\dfrac{3}{4}:\dfrac{5}{8}\)
\(?=\dfrac{3}{4}\times\dfrac{8}{5}\)
\(?=\dfrac{6}{5}\)
c) \(?\times\dfrac{6}{11}=1\)
\(?=1:\dfrac{6}{11}\)
\(?=1\times\dfrac{11}{6}\)
\(?=\dfrac{11}{6}\)
Rút gọn rồi tính.
a) \(\dfrac{2}{4}\times\dfrac{9}{5}\) b) \(\dfrac{13}{8}\times\dfrac{5}{15}\) c) \(\dfrac{3}{9}\times\dfrac{6}{12}\)
a) \(\dfrac{2}{4}\times\dfrac{9}{5}=\dfrac{1}{2}\times\dfrac{9}{5}=\dfrac{1\times9}{2\times5}=\dfrac{9}{10}\)
b) \(\dfrac{13}{8}\times\dfrac{5}{15}=\dfrac{13}{8}\times\dfrac{1}{3}=\dfrac{13}{24}\)
c) \(\dfrac{3}{9}\times\dfrac{6}{12}=\dfrac{1}{3}\times\dfrac{1}{2}=\dfrac{1}{3\times2}=\dfrac{1}{6}\)
a: =18/20=9/10
b: \(=\dfrac{13\cdot5}{8\cdot15}=\dfrac{13}{8}\cdot\dfrac{1}{3}=\dfrac{13}{24}\)
c: \(=\dfrac{1}{3}\cdot\dfrac{1}{2}=\dfrac{1}{6}\)
A = \(\dfrac{-19}{9}\times\dfrac{1}{2}-\dfrac{4}{11}\times\dfrac{-11}{9}+\left(-\dfrac{2}{3}\right)\)
B = \(\left(-\dfrac{15}{6}\right)\div\dfrac{-1}{2}+\dfrac{7}{-12}-\dfrac{1}{3}\times\dfrac{-11}{2}\)
C = \(\dfrac{3}{4}\times\left(-8\right)-\dfrac{1}{3}\times\dfrac{-7}{2}-\dfrac{5}{18}\)
\(A=\dfrac{-19}{9}.\dfrac{1}{2}-\dfrac{4}{11}.\dfrac{-11}{9}+\left(-\dfrac{2}{3}\right)=-\dfrac{23}{18}\)
\(B=\left(-\dfrac{15}{6}\right):\dfrac{-1}{2}+\dfrac{7}{-12}-\dfrac{1}{3}.\dfrac{-11}{2}=\dfrac{25}{4}\)
\(C=\dfrac{3}{4}.\left(-8\right)-\dfrac{1}{3}.\dfrac{-7}{2}-\dfrac{5}{18}=-\dfrac{46}{9}\)
\(A=\dfrac{-19}{18}+\dfrac{4}{9}-\dfrac{2}{3}=\dfrac{-19}{18}+\dfrac{8}{18}-\dfrac{12}{18}=\dfrac{-23}{18}\)
\(B=\dfrac{-5}{2}\cdot\dfrac{-2}{1}-\dfrac{7}{12}+\dfrac{11}{6}=\dfrac{5\cdot12-7+22}{12}=\dfrac{75}{12}=\dfrac{25}{4}\)
Tính bằng cách thuận tiện.
a) \(\dfrac{3}{5}\times\dfrac{7}{11}\times\dfrac{5}{3}\times11\)
b) \(\dfrac{3}{8}\times\dfrac{2}{7}+\dfrac{5}{7}\times\dfrac{3}{8}\)
a)
\(\dfrac{3}{5}\times\dfrac{7}{11}\times\dfrac{5}{3}\times11\\ =\left(\dfrac{3}{5}\times\dfrac{5}{3}\right)\times\left(\dfrac{7}{11}\times11\right)\\ =\dfrac{3\times5}{5\times3}\times\dfrac{7\times11}{11}\\ =1\times7\\ =7\)
b)
\(\dfrac{3}{8}\times\dfrac{2}{7}+\dfrac{5}{7}\times\dfrac{3}{8}\\ =\dfrac{3}{8}\times\left(\dfrac{2}{7}+\dfrac{5}{7}\right)\\ =\dfrac{3}{8}\times\dfrac{7}{7}\\ =\dfrac{3}{8}\times1=\dfrac{3}{8}\)
Tính (theo mẫu):
a) \(\dfrac{5}{6}\times7\) b) \(\dfrac{7}{10}\times3\) c) \(5\times\dfrac{4}{21}\) d) \(2\times\dfrac{5}{9}\)
a: \(\dfrac{5}{6}\cdot7=\dfrac{5\cdot7}{6}=\dfrac{35}{6}\)
b: \(\dfrac{7}{10}\cdot3=\dfrac{7\cdot3}{10}=\dfrac{21}{10}\)
c: \(5\cdot\dfrac{4}{21}=\dfrac{5\cdot4}{21}=\dfrac{20}{21}\)
d: \(2\cdot\dfrac{5}{9}=\dfrac{2\cdot5}{9}=\dfrac{10}{9}\)
Rút gọn rồi tính:
a) \(\dfrac{3}{9}\times\dfrac{5}{4}\) b) \(\dfrac{10}{15}\times\dfrac{3}{5}\) c) \(\dfrac{5}{8}\times\dfrac{4}{12}\) d) \(\dfrac{9}{27}\times\dfrac{3}{21}\)
a: \(\dfrac{3}{9}\times\dfrac{5}{4}=\dfrac{5}{4}\times\dfrac{1}{3}=\dfrac{5\times1}{4\times3}=\dfrac{5}{12}\)
b: \(\dfrac{10}{15}\times\dfrac{3}{5}=\dfrac{3}{5}\times\dfrac{2}{3}=\dfrac{3\times2}{5\times3}=\dfrac{2}{5}\)
c: \(\dfrac{5}{8}\times\dfrac{4}{12}=\dfrac{5}{8}\times\dfrac{1}{3}=\dfrac{5}{3\times8}=\dfrac{5}{24}\)
d: \(\dfrac{9}{27}\times\dfrac{3}{21}=\dfrac{1}{7}\times\dfrac{1}{3}=\dfrac{1\times1}{7\times3}=\dfrac{1}{21}\)