1. Suppose P is a 5x4 matrix, Q is an nxm matrix and R is a 3x2 matrix. If (QR)T P is defined then ... a) n=4, m=3 or b) n=4, m=2 I have no idea what to do. This is basic stuff... I am doing a correspondence course (no lecturers to help), so I am stuck at this and some of my other questions. Where do I start in solving this? I really want to grasp linear algebra and not just get an answer. I know that a 5x4 matrix has 5 rows and 4 columns and that is = P. What do they mean by (QR)T? I think that someone who understands this will easily see what they are referring to and unfortunately I am not there at the moment.