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Lời giải:
$B=\frac{3}{2}-\frac{2}{21}-\frac{7}{12}+\frac{15}{21}-\frac{1}{3}+\frac{5}{4}-\frac{2}{7}-\frac{1}{3}$
$=(\frac{3}{2}+\frac{5}{4})+(\frac{-2}{21}+\frac{15}{21}+\frac{-2}{7})+(\frac{-7}{12}+\frac{-1}{3}+\frac{-1}{3})$
$=\frac{11}{4}+\frac{1}{3}-\frac{5}{4}=\frac{11}{6}$
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( \(\dfrac{1}{2}\) - \(\dfrac{13}{14}\)): \(\dfrac{5}{7}\) - (- \(\dfrac{2}{21}\) + \(\dfrac{1}{7}\)) : \(\dfrac{5}{7}\)
(\(\dfrac{7}{14}\) - \(\dfrac{13}{14}\)): \(\dfrac{5}{7}\) - ( - \(\dfrac{2}{21}\) + \(\dfrac{3}{21}\)): \(\dfrac{5}{7}\)
- \(\dfrac{6}{14}\): \(\dfrac{5}{7}\) - \(\dfrac{1}{21}\): \(\dfrac{5}{7}\)
= - (\(\dfrac{3}{7}\) + \(\dfrac{1}{21}\)): \(\dfrac{5}{7}\)
= -\(\dfrac{10}{21}\): \(\dfrac{5}{7}\)
= - \(\dfrac{2}{3}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(2\frac{7}{19}-3\frac{5}{21}+7-\frac{7}{19}+2\frac{5}{21}\)
\(=2+\frac{7}{19}-3-\frac{5}{21}+7-\frac{7}{19}+2+\frac{5}{21}\)
\(=\left(2-3+7+2\right)+\left(\frac{7}{19}-\frac{7}{19}\right)+\left(\frac{5}{21}-\frac{5}{21}\right)\)
\(=2-3+7+2+0+0=8\)
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b) \(\frac{\frac{2}{3}+\frac{5}{7}+\frac{4}{21}}{\frac{5}{6}+\frac{11}{7}-\frac{7}{21}}\)
\(=\frac{\frac{29}{21}+\frac{4}{21}}{\frac{101}{42}-\frac{7}{21}}\)
\(=\frac{\frac{11}{7}}{\frac{29}{14}}\)
\(=\frac{22}{29}.\)
Chúc bạn học tốt!
![](https://rs.olm.vn/images/avt/0.png?1311)
\(\frac{28}{23}+\frac{19}{21}-\frac{5}{23}+\frac{7}{10}+\frac{2}{21}\)
\(=\left(\frac{28}{23}-\frac{5}{23}\right)+\left(\frac{19}{21}+\frac{2}{21}\right)+\frac{7}{10}\)
\(=\frac{23}{23}+\frac{21}{21}+\frac{7}{10}\)
\(=1+1+\frac{7}{10}=2\frac{7}{10}=2,7\)
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\(=\dfrac{3}{2}-\dfrac{2}{21}-\dfrac{7}{12}+\left[\dfrac{15}{21}-\dfrac{1}{3}+\dfrac{5}{4}-\dfrac{2}{7}-\dfrac{1}{3}\right]\)
=11/12-2/21+5/7-2/3+5/4-2/7
=11/12-2/3+5/4-2/21+3/7
=11/12-8/12+15/12-2/21+9/21
=18/12+7/21
=3/2+1/3
=9/6+2/6=11/6
-2/5+7/21
=-42/105+35/105
=-7/105 = -1/15
bằng -1 phần 5 nhé