If a matrix A is 5 x 3 and the product AB is 5 x 7, what is the size of B?
Matrix Multiplication
Two matrices may be multiplied if and only if the first matrix has the same number of columns as there are rows in the second matrix. Suppose the first matrix has dimensions of a×b and the second matrix has dimensions of c×d, we can say that b=c and their product will have dimensions of a×d