This has been covered ad nauseum elsewhere in the financial press, but you're assuming Yahoo pays zero corporate taxes on its sale of Alibaba shares. That's not how the world works. You need to deduct something like 40% from the value of the "Cash from Alibaba sale" and "Value of remaining Alibaba stock" and probably also "Value of Yahoo Japan stock". My bet is if you do that, you'll come up with a number that makes sense given Yahoo's market price.