\(\frac{3}{5}\times\frac{7}{21}+\frac{7}{21}\times\frac{2}{5}=\frac{7}{21}\times\left(\frac{3}{5}+\frac{2}{5}\right)=\frac{1}{3}\times\left(\frac{3}{5}+\frac{2}{5}\right)=\frac{1}{3}\times1=\frac{1}{3}\)
Học tốt !
\(\frac{3}{5}\cdot\frac{7}{21}+\frac{7}{21}+\frac{2}{5}\)
\(=\frac{7}{21}\cdot(\frac{3}{5}+\frac{2}{5})\)
\(=\frac{7}{21}\cdot1=\frac{7}{21}=\frac{1}{3}\)
C1 \(\frac{3}{5}.\frac{7}{21}+\frac{7}{21}.\frac{2}{5}\)
\(=\frac{7}{21}\left(\frac{3}{5}+\frac{2}{5}\right)\)
\(=\frac{7}{21}.1\)
\(=\frac{7}{21}=\frac{1}{3}\)
C2 \(\frac{3}{5}.\frac{7}{21}+\frac{7}{21}.\frac{2}{5}\)
\(=\frac{3.7}{5.21}+\frac{7.2}{21.5}\)
\(=\frac{21}{105}+\frac{14}{105}\)
\(=\frac{35}{105}\)
\(=\frac{7}{21}=\frac{1}{3}\)
Cách 1:
=7/21 x (3/5 + 2/5)
=7/21 x 1
= 7/21 = 1/3
Cách 2
=1/5 + 2/15
=3/15 +2/15
=5/15 = 1/3
Cách 2 :
\(\frac{3}{5}\times\frac{7}{21}+\frac{7}{21}\times\frac{2}{5}=\frac{3}{5}\times\frac{1}{3}+\frac{1}{3}\times\frac{2}{5}=\frac{1}{5}+\frac{2}{15}=\frac{1}{3}\)
\(\frac{3}{5}\cdot\frac{7}{21}+\frac{7}{21}\cdot\frac{2}{5}\)
\(=\frac{3\cdot7}{5\cdot21}+\frac{7\cdot2}{21\cdot5}\)
\(=\frac{3\cdot7}{5\cdot3\cdot7}+\frac{14}{105}\)
\(=\frac{1}{5}+\frac{14}{105}=\frac{21}{105}+\frac{14}{105}=\frac{35}{105}=\frac{1}{3}\)
