Tính giá trị biểu thức

$$\begin{gathered} \mathrm{a}) \mathrm{D}=\begin{array}{c}1\\ 2.3\end{array}+\begin{array}{c}1\\ 3.4\end{array}+\begin{array}{c}1\\ 4.5\end{array}+.....+\begin{array}{c}1\\ 19.20\end{array} \\ \mathrm{b}) \mathrm{E}= \begin{array}{c}1\\ 99\end{array}-\begin{array}{c}1\\ 99.98\end{array}-\begin{array}{c}1\\ 98.97\end{array}-\begin{array}{c}1\\ 97.96\end{array}......\begin{array}{c}1\\ 3.2\end{array}-\begin{array}{c}1\\ 2.1\end{array} \end{gathered}$$

giúp mik mng oii :<<