why does (-5)*(-4)=20 ?, eom

[John V]

There is a real and simple answer to this. Go back to first grade. Remember the number line?

5 means five units to the right - right is the default.

5*4 means you go five units to the right four times, and end up at 20.

-5 means five units to the left. The negative sign reverses direction.

(-5)*4 means you go 5 units to the left four times, and end up at -20.

With (-5)*(-4), the first minus reverses direction from the default right and has you going left. The second minus reverses direction again, and has you going right.