A matrix A is identified as [tex]A _{r*c} [/tex] and matrix B is identified as [tex]B _{r*c} [/tex].If the number of columns in A is the same as the number of rows in B, then you can multiply the matrices together. The product matrix, then, is made up of what's left over: rows from A and columns from B. So your answers above are, in the first blank: columns, and in the second blank: rows.