Numbers of zero entries in matrix direct sum

Question

Let $A_0,\dots,A_n$ be matrices in $\operatorname{Mat}_{M_0\times N_0},\dots,\operatorname{Mat}_{M_n\times N_n}$, respectively, all with no zero entries. Then how many non-zero entries does $\oplus_{i=0}^n A_i$ have; where the matrix direct sum is defined here.

Answer 1

$A_i$ has $M_iN_i$ non zero entries, hence $\oplus_{i=0}^n A_i$ has $\sum_{i=0}^nM_iN_i$ non zero entries.$