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Trả lời bởi giáo viên
Đáp án đúng:
C. \(\dfrac{{5}}{{7}}\)
$\begin{array}{l}\dfrac{5}{7} \times \dfrac{{11}}{{18}} + \dfrac{7}{{18}} \times \dfrac{5}{7} = \dfrac{5}{7} \times \left( {\dfrac{{11}}{{18}} + \dfrac{7}{{18}}} \right)\\\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = \dfrac{5}{7} \times \dfrac{8}{{18}}\\\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = \dfrac{5}{7} \times 1\,\\\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = \,\,\,\,\dfrac{5}{7}\end{array}$
Hướng dẫn giải:
Áp dụng tính chất phân phối của phép nhân: \(a \times (b + c) = a \times b + a \times c\).
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