How much DNA do siblings share?

[gim]

I figured, and it seems to be right, that on average, siblings will have 50% of their DNA in common. The words "on average" are important here, because they may share more or less that 50% of their DNA.

 

What I can't figure out is this. Say I have two siblings. If I look at their combined DNA, how much of it will be the same as mine (on average)? Obviously more than 50%, but less than 100%. This is a statistical thing, and I would like to be shown how to work it out.

 

Thanks,

Greg.

[SRHBRU]

Click on the link and scroll down. It will tell you the percentages of the relationships.

 

http://freepages.genealogy.rootsweb.ancestry.com/~laetoli/degree.html