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a, \(\frac{1}{2}x\frac{2}{7}+\frac{3}{7}:2+\frac{1}{2}:\frac{7}{2}\)
= \(\frac{1}{2}x\frac{2}{7}+\frac{3}{7}x\frac{1}{2}+\frac{1}{2}x\frac{2}{7}\)
= \(\frac{1}{2}x\left(\frac{2}{7}+\frac{3}{7}+\frac{2}{7}\right)\)
= \(\frac{1}{2}x1\)
= \(\frac{1}{2}\)
\(a,\frac{1}{2}x\frac{2}{7}+\frac{3}{7}:2+\frac{1}{2}:\frac{7}{2}\)
\(=\frac{1}{2}x\frac{2}{7}+\frac{3}{7}x\frac{1}{2}+\frac{1}{2}x\frac{2}{7}\)
\(=\frac{1}{2}x\left(\frac{2}{7}+\frac{3}{7}+\frac{2}{7}\right)\)
\(=\frac{1}{2}x1\)
\(=\frac{1}{2}\)
\(b,\frac{3}{7}x\frac{3}{5}+\frac{3}{5}:7+\frac{3}{7}:\frac{5}{3}\)
\(=\frac{3}{7}x\frac{3}{5}+\frac{3}{5}x\frac{1}{7}+\frac{3}{7}x\frac{3}{5}\)
\(=\frac{3}{5}x\left(\frac{3}{7}+\frac{1}{7}+\frac{3}{7}\right)\)
\(=\frac{3}{5}x1\)
\(=\frac{3}{5}\)
\(\left(\frac{2}{3}+\frac{1}{3}:\frac{3}{4}+\frac{5}{9}\right).y-3=25\%+\frac{7}{4}\)
\(\Rightarrow\left(\frac{2}{3}+\frac{4}{9}+\frac{5}{9}\right).y-3=\frac{1}{4}+\frac{7}{4}\)
\(\Rightarrow\left(\frac{2}{3}+1\right).y-3=2\)
\(\Rightarrow\frac{5}{3}.y-3=2\)
\(\Rightarrow y-3=2:\frac{5}{3}\)
\(\Rightarrow y-3=\frac{6}{5}\)
\(\Rightarrow y=\frac{6}{5}+3\)
\(\Rightarrow y=\frac{21}{5}\)
a. =(1+10)×10 :2
=11×10:2
=110:2
=55
b. Số các số hạng là =(90-9):9+1= 10
Tổng = (9+90)×10:2=495
ket qua =1/2