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a,
x.2/7.3/4=5/21
x.3/14=5/21
x=5/21:3/14
x=10/9
b,
x.1/2=1/3
x=1/3:1/2
x=2/3
c,
x:4/5=25/8:5/4
x:4/5=5/2
x=5/2.4/5=2
A, x= 5/25 : 3/4 : 2/7 = 14/15
B, x=1/3 : 1/2 = 2/3
C, x=(25/8 : 5/4)x4/5 = 5/2 x 4/5 = 2
\(\frac{2}{3}.\frac{4}{5}+\frac{1}{3}.\frac{4}{5}=\frac{4}{5}\left(\frac{2}{3}+\frac{1}{3}\right)=\frac{4}{5}.\frac{3}{3}=\frac{4}{5}.1=\frac{4}{5}\)
\(\frac{1}{2}:\frac{3}{4}+\frac{1}{6}:\frac{3}{4}=\frac{3}{4}:\left(\frac{1}{2}+\frac{1}{6}\right)=\frac{3}{4}:\frac{2}{3}=\frac{9}{8}\)
\(\frac{2}{3}.\frac{4}{5}-\frac{1}{3}.\frac{4}{5}=\frac{4}{5}\left(\frac{2}{3}-\frac{1}{3}\right)=\frac{4}{5}.\frac{1}{3}=\frac{4}{15}\)
\(\frac{1}{2}:\frac{3}{4}-\frac{1}{6}:\frac{3}{4}=\frac{3}{4}:\left(\frac{1}{2}-\frac{1}{6}\right)=\frac{3}{4}:\frac{1}{3}=\frac{9}{4}\)
\(\frac{2}{3}.\frac{4}{5}+\frac{1}{3}.\frac{4}{5}=\left(\frac{2}{3}+\frac{1}{3}\right).\frac{4}{5}=1.\frac{4}{5}=\frac{4}{5}\)
\(\frac{1}{2}:\frac{3}{4}+\frac{1}{6}:\frac{3}{4}=\frac{1}{2}.\frac{4}{3}+\frac{1}{6}.\frac{4}{3}=\left(\frac{1}{2}+\frac{1}{6}\right).\frac{4}{3}=\frac{2}{3}.\frac{4}{3}=\frac{8}{9}\)
c,d tương tự
\(\frac{6:\frac{3}{5}-1\frac{1}{6}\cdot\frac{6}{7}}{4\frac{1}{5}\cdot\frac{10}{11}+5\frac{2}{11}}=1\)
\(\frac{6:\frac{3}{5}-1\frac{1}{6}.\frac{6}{7}}{4\frac{1}{5}.\frac{10}{11}+5\frac{2}{11}}=\frac{10-\frac{7}{6}.\frac{6}{7}}{\frac{21}{5}.\frac{10}{11}+\frac{57}{11}}=\frac{10-1}{\frac{42}{11}+\frac{57}{11}}=\frac{9}{9}=1\)
\(\frac{5}{3}\cdot\frac{4}{7}\cdot\frac{3}{5}\cdot\frac{7}{8}\)
\(=\frac{1}{2}\)
128.72 + 14.256
= 128.72 + 14.2.128
= 128.(72 + 14.2)
= 128.100
= 12800
\(\frac{5}{3}\cdot\frac{4}{7}\cdot\frac{3}{5}\cdot\frac{7}{8}\)
\(=\left(\frac{5}{3}\cdot\frac{3}{5}\right)\cdot\left(\frac{4}{7}\cdot\frac{7}{8}\right)\)
\(=1\cdot\frac{1}{2}\)
\(=\frac{1}{2}\)
\(128\cdot72+14\cdot256\)
\(=128\cdot2\cdot36+14\cdot256\)
\(=256\cdot36+14\cdot256\)
\(=256\cdot\left(36+14\right)\)
\(=256\cdot50\)
\(=12800\)
Học tốt #
\(\frac{9}{14}.y=\frac{7.4}{14.7}\)
\(\frac{9}{14}.y=\frac{1.2}{7.1}\)
\(\frac{9}{14}.y=\frac{2}{7}\)
\(y=\frac{2}{7}:\frac{9}{14}=\frac{2}{7}.\frac{14}{9}\)
\(y=\frac{2.2}{1.9}=\frac{4}{9}\)
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Ta có : \(\frac{9}{14}y=\frac{7}{14}.\frac{4}{7}\)
\(\Rightarrow\frac{9}{14}y=\frac{2}{7}\)
\(\Rightarrow y=\frac{2}{7}.\frac{14}{9}\)
\(\Rightarrow y=\frac{4}{9}\)
Đặt \(A=\frac{4}{3}\cdot\frac{4}{7}+\frac{4}{7}\cdot\frac{4}{11}+...+\frac{4}{95}\cdot\frac{4}{99}\)
\(A=\frac{16}{21}+\frac{16}{77}+...+\frac{16}{9405}\)
\(A=\frac{16}{3\cdot7}+\frac{16}{7\cdot11}+....+\frac{16}{95\cdot99}\)
\(A=\frac{16}{4}\cdot\left(\frac{1}{3}-\frac{1}{7}+\frac{1}{7}-\frac{1}{11}+...+\frac{1}{95}-\frac{1}{99}\right)\)
\(A=4\cdot\left(\frac{1}{3}\cdot\frac{1}{99}\right)=4\cdot\frac{32}{99}=\frac{128}{99}\)