Hãy tính ​\(D = \dfrac{3}{7}.\dfrac{2}{5}.\dfrac{7}{3}.20.\dfrac{{19}}{{72}}\)

Câu hỏi :

Tính \(D = \dfrac{3}{7}.\dfrac{2}{5}.\dfrac{7}{3}.20.\dfrac{{19}}{{72}}\)

A.  \(\dfrac{{19}}{9} \)

B.  \(\dfrac{{9}}{19}\)

C.  \(-\dfrac{{9}}{2}\)

D.  \(\dfrac{{-5}}{18}\)

* Đáp án

A

* Hướng dẫn giải

Ta có: 

\(\begin{array}{l}D = \dfrac{3}{7}.\dfrac{2}{5}.\dfrac{7}{3}.20.\dfrac{{19}}{{72}}\\ = \left( {\dfrac{3}{7}.\dfrac{7}{3}} \right).\dfrac{2}{5}.20.\dfrac{{19}}{{72}}\\ = 1.\dfrac{2}{5}.20.\dfrac{{19}}{{72}}\\ = \dfrac{{19}}{9}\end{array}\)

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