I like number theory stuff like this, so I'll do a bit of my own. I took a 1320x1600 picture by Fel, saved it at 100, 90, 80, 70, 60, and 50% zooms with 95% quality JPEGs each time. The results are as follows
At 100% zoom it is 100% the image size and 100% the file size.
At 90% zoom it is...