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2.
\(\frac{3}{5}-\)\(\frac{1}{3}\text{x}=\frac{1}{2}\)
\(\frac{1}{3}x=\frac{1}{2}+\frac{3}{5}\)
\(\frac{1}{3}x=\frac{11}{10}\)
\(x=\frac{11}{10}:\frac{1}{3}=\frac{11}{10}\text{x}\frac{3}{1}\)
\(x=\frac{33}{10}\)
\(B=\frac{2}{8}+\frac{2}{24}+\frac{2}{48}+...+\frac{2}{18\cdot20}\)
\(B=\frac{2}{2\cdot4}+\frac{2}{4\cdot6}+\frac{2}{6\cdot8}+...+\frac{2}{18\cdot20}\)
\(B=\frac{1}{2}-\frac{1}{4}+\frac{1}{4}-\frac{1}{6}+\frac{1}{6}-\frac{1}{8}+...+\frac{1}{18}-\frac{1}{20}\)
\(B=\frac{1}{2}-\frac{1}{20}\)
\(B=\frac{9}{20}\)
=))
\(A=\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+\frac{1}{30}+\frac{1}{42}+\frac{1}{56}+\frac{1}{72}+\frac{1}{90}\)
\(A=\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+\frac{1}{5.6}+\frac{1}{6.7}+\frac{1}{7.8}+\frac{1}{8.9}+\frac{1}{9.10}\)
\(A=\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{9}-\frac{1}{10}\)
\(A=\frac{1}{2}+\left(\frac{1}{3}-\frac{1}{3}\right)+\left(\frac{1}{4}-\frac{1}{4}\right)+...+\left(\frac{1}{9}-\frac{1}{9}\right)-\frac{1}{10}\)
\(A=\frac{1}{2}-\frac{1}{10}=\frac{2}{5}\)
25/49 x 21/29 - 25/49 x 7/29 + 24/29
= 25/49 x ( 21/ 29 - 7/29 ) + 24/49
= 25/49 x 14/29 + 24/29
= 350/1421 + 24/29
= 350/1421 + 1176/1421
= 1526/1421
\(\frac{25}{49}\times\frac{21}{29}-\frac{25}{49}\times\frac{7}{29}+\frac{24}{49}\)
\(=\frac{25\times\left(21-7\right)}{49\times29}+\frac{24}{49}\)
\(\frac{50}{7\times29}+\frac{24}{49}=\frac{2450+4872}{7\times29\times49}=\frac{7322}{7\times29\times49}=\frac{1046}{1421}\)
\(a,\frac{57}{300}=\frac{19}{100}=19\%\)
\(b,\frac{24}{400}=\frac{6}{100}=6\%\)
\(c,\frac{12}{500}=\frac{2.4}{100}=2,4\%\)
\(d,\frac{750}{600}=\frac{125}{100}=125\%\)
~Study well~
#๖ۣۜNamiko#
GIẢI
a) \(\frac{57}{300}=\frac{19}{100}=19\%\)
b) \(\frac{24}{400}=\frac{6}{100}=6\%\)
c)\(\frac{12}{500}=\frac{6}{250}=2,4\%\)
d )\(\frac{750}{600}=\frac{125}{100}=125\%\)
P/S: HOK TỐT !
\(=\frac{4}{2x4}+\frac{4}{4x6}+\frac{4}{6x8}+...+\frac{4}{18x20}\)
\(=2\left(\frac{1}{2}-\frac{1}{4}+\frac{1}{4}-\frac{1}{6}+...+\frac{1}{18}-\frac{1}{20}\right)\)
\(=2x\left(\frac{1}{2}-\frac{1}{20}\right)\\ =2x\frac{9}{20}\\ =\frac{9}{10}\)