Toán Lớp 5: 4/7 : 2/5 + 3/7 : 2/5 – 7/9
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Toán Lớp 5: 4/7 : 2/5 + 3/7 : 2/5 – 7/9
tính bằng cách thuận tiênj
Comments ( 2 )
\frac{4}{7}:\frac{2}{5} + \frac{3}{7}:\frac{2}{5} – \frac{7}{9}\\
= \left( {\frac{4}{7} + \frac{3}{7}} \right):\frac{2}{5} – \frac{7}{9}\\
= \frac{7}{7}:\frac{2}{5} – \frac{7}{9}\\
= 1 \times \frac{5}{2} – \frac{7}{9}\\
= \frac{5}{2} – \frac{7}{9}\left( {MSC:18} \right)\\
= \frac{{5 \times 9}}{{2 \times 9}} – \frac{{7 \times 2}}{{9 \times 2}}\\
= \frac{{45}}{{18}} – \frac{{14}}{{18}}\\
= \frac{{45 – 14}}{{45}}\\
= – \frac{{31}}{{18}}
\end{array}\]