What is the determinant of the matrix $\begin{bmatrix} 10 & 8 \\ 20 & 12 \end{bmatrix} $ ?

$-40$

$-6$

$40$

$104$

$160$

Approach 1

The determinant of a two by two matrix:

$$ \text{det}\begin{bmatrix} a & b \\ c & d \end{bmatrix} = ad-bc $$ $$ \text{det}\begin{bmatrix} 10 & 8 \\ 20 & 12 \end{bmatrix} = 10\cdot12 - 8\cdot 20 $$ $$ = 120-160 = \boxed{-40}$$

Approach 2

Determinants can be calculated using your calculator. The instructions for each type of calculator varies.