\(\dfrac{2}{3}+\dfrac{1}{5}.\dfrac{10}{7}=\dfrac{2}{3}+\dfrac{10}{35}=\dfrac{70}{105}+\dfrac{30}{105}=\dfrac{100}{105}=\dfrac{50}{21}\)
a) Ta có: \(\dfrac{2}{3}+\dfrac{1}{5}\cdot\dfrac{10}{7}\)
\(=\dfrac{2}{3}+\dfrac{2}{7}\)
\(=\dfrac{14}{21}+\dfrac{6}{21}\)
\(=\dfrac{20}{21}\)
\(\dfrac{7}{12}-\dfrac{27}{7}.\dfrac{1}{8}=\dfrac{7}{12}-\dfrac{27}{56}=\dfrac{392}{672}-\dfrac{324}{672}=\dfrac{68}{672}=\dfrac{17}{168}\)
b) Ta có: \(\dfrac{7}{12}-\dfrac{27}{7}\cdot\dfrac{1}{8}\)
\(=\dfrac{7}{12}-\dfrac{27}{56}\)
\(=\dfrac{98}{168}-\dfrac{81}{168}\)
\(=\dfrac{17}{168}\)
c) Ta có: \(\dfrac{5}{9}\cdot\dfrac{7}{13}+\dfrac{5}{9}\cdot\dfrac{9}{13}-\dfrac{3}{13}\cdot\dfrac{5}{9}\)
\(=\dfrac{5}{9}\left(\dfrac{7}{13}+\dfrac{9}{13}-\dfrac{3}{13}\right)\)
\(=\dfrac{5}{9}\cdot1=\dfrac{5}{9}\)
\(\dfrac{5}{9}.\dfrac{7}{13}+\dfrac{5}{9}.\dfrac{9}{13}-\dfrac{3}{13}.\dfrac{5}{9}=\dfrac{35}{117}+\dfrac{5}{13}-\dfrac{5}{39}=\dfrac{5}{9}\)
\(\dfrac{5}{9}.\dfrac{7}{13}+\dfrac{5}{9}.\dfrac{9}{13}-\dfrac{3}{13}.\dfrac{5}{9}=\dfrac{5}{9}\left(\dfrac{7}{13}+\dfrac{9}{13}-\dfrac{3}{13}\right)=\dfrac{5}{9}.\dfrac{13}{13}=\dfrac{5}{9}\)
2/3+1/5x10/7=2/3+10/35=70/105+30/105=50/21
Giải:
a)2/3+1/5.10/7
=2/3+2/7
=20/21
b)7/12-27/7.1/8
=7/12-27/56
=17/168
c)5/9.7/13+5/9.9/13-3/13.5/9
=5/9.(7/13+9/13-3/13)
=5/9.1
Chúc bạn học tốt!
\(\dfrac{2}{3}\)+\(\dfrac{1}{5}\).\(\dfrac{10}{7}\)=\(\dfrac{2}{3}\)+\(\dfrac{10}{35}\)=\(\dfrac{70}{105}\)+\(\dfrac{30}{105}\)=\(\dfrac{100}{105}\)=\(\dfrac{50}{21}\)=\(\dfrac{2}{8}21\).