# Weird GRE mistake [duplicate]

According to the answer key, the correct answer is (a).... This is obviously a mistake, right? If a square matrix is invertible, then it has full rank.

• Well B, C, D and E are all equivalent, and B implies A, but not vice versa. Jul 23, 2017 at 14:40
• But is a saying it has full rank?
– user223391
Jul 23, 2017 at 14:41
• Nope, it is not. :) Jul 23, 2017 at 14:43
• @SihOASHoihd This might help math.stackexchange.com/questions/6734/… Jul 23, 2017 at 14:43

$$\begin{bmatrix} 1 & 0 & 0 & 0 & 1 \\ 0 & 1 & 0 & 0 & 1 \\ 0 & 0 & 1 & 0 & 1 \\ 0 & 0 & 0 & 1 & 1 \\ 0 & 0 & 0 & 0 & 0 \end{bmatrix}$$