So, you are saying faturnal twins are a 8 in 1000, at least in the US.. so 1 per 125 births is whats missing?
Even adding that to the mix, I still don't see how 1 in 125 to have fraternal twins, comined with the 1 in 4 for white, 1 in 4 for black and 1 in 2 for biracial gets you to 1 in 1 Million.
Damn FRATERNAL.. ouch... need some coffee.
Well, for what it's worth, here's how the Daily Mail calculated it:
http://www.snopes.com/photos/people/mixedtwins.asp