Solution
= Solution
The vector of column <sample means> is $\bar x=(1,3,2)$. Subtract it from each observation. The centred data matrix, with cell types in the original order, is
$$
\boxed{X_c=\begin{pmatrix}-1&-3&-2\\-1&1&-2\\-1&1&2\\3&1&2\end{pmatrix}}.
$$
Each column now has <sample mean> zero.