Tính: \(\,D = \frac{1}{2}.\frac{{250}}{{17}} + \frac{1}{2}.\frac{{90}}{{17}}\)

* Hướng dẫn giải

\(\begin{array}{l}\,D = \frac{1}{2}.\frac{{250}}{{17}} + \frac{1}{2}.\frac{{90}}{{17}} = \frac{1}{2}.\left( {\frac{{250}}{{17}} + \frac{{90}}{{17}}} \right)\\\,\,\,\,\,\,\,\,\,\,\,\, = \frac{1}{2}.\frac{{340}}{{17}} = \frac{1}{2}.20 = 10\end{array}\)

Chọn D