Darn you're quick Steve

I see the logic in 2 exposures of 1/125 or 4 of 1/250. I see what I did wrong. 1/20 + 1/40 isn't 1/60, it's about 1/13th of a second. 2x 1/125 = 1/62,5 (calculated a bit over exposed)

What if I shoot ones 1/125 and twice 1/250? Same result as 1/60?

Is it possible to make an uneven division of the two exposures to create a HDR picture? Or can HDR only be created after taking two seperate pictures?