Discrete vs continuous variable
Prove
\[\sum_{i=1}^k abx_i = ab \sum_{i=1}^k x_i\]
\[\prod_{i=1}^n c =c^n\]
Find the value of
\[\sum_{i=1}^{10} (x_i-4)\]
where
\[\sum_{i=1}^{10}=20\]