partially transparent layers when using alpha over/ mix

can’t figure out why mixing layers in compositing I’m getting transparent images when set to .5 . I figured alpha over would quickly fix problem but same thing. I watched some tutorials but I don’t see how what I’m doing is any different.

A 0.5 mix is 50% of one, 50% of another, so it is expected to see both sources with partial transparency. With alpha over it depends on the alpha channel of top image, if alpha is not solid (1.0) that pixel will contain 1-alpha ratio of background.

What do you have as source images, what do you want to achieve? Post some screenshots, it is easier to give advice if we actually see something.