Matrix addition and multiplication

A question from Yahoo! Answers:

Any matrix that is conformable for multiplication will also be conformable for addition.?

No. You can only add matrices of the same size. You can only multiply matrices if the number of columns in the first marix is equal to the number of rows in the second matrix.

Sources:

http://mathworld.wolfram.com/MatrixAddit…
http://mathworld.wolfram.com/MatrixMulti…