\begin{frame}
  \frametitle{Computing with Sums}

  \begin{block}{}
    \begin{malign}
      \sum_{i=1}^n c &= \mpause[1]{nc} \\
      \mpause{\sum_{i=1}^n ca_i &=} \mpause{c \sum_{i=1}^n a_i} \\
      \mpause{\sum_{i=1}^n (a_i + b_i) &=} \mpause{\sum_{i=1}^n a_i + \sum_{i=1}^n b_i} \\
      \mpause{\sum_{i=1}^n (a_i - b_i) &=} \mpause{\sum_{i=1}^n a_i - \sum_{i=1}^n b_i} 
    \end{malign}
  \end{block}
  \pause[9]
  
  \begin{block}{}
    \begin{malign}
      \sum_{i=1}^n i &= \frac{n(n+1)}{2}  &
      \sum_{i=1}^n i^2 &= \frac{n(n+1)(2n+1)}{6}
    \end{malign}
  \end{block}  
\end{frame}