# Matrix multiplication

In this quiz, the correct answer is "all of the above".
But I don't understand how B is correct.

1 answers ( 0 marked as helpful)

Hi Lisa,
to be honest with you, the phrasing on the question could be a bit more precise.
What is meant in b) is: You multiply two incompatible matrices.
Because of course, matrix multiplication of matrices A * B, requires A to have dimensions of (mxn) and B to be of size (nxm) for them to be compatible. This of course means that if m and n are not equal, the matrices are of different sizes, multiplying them however, requires no recycling.
In addition, the answer in a) should read : You multiple a matrix by a vector, when the two are incompatible
For instance, multiplying a mxn matrix by a nx1 vector requires no recycling.
Thanks for asking the question and sorry for the confusion!
Best,
365 Eli