That particular report is a bit confusing: first it says 29% of all americans own one or the other. That would be around 100 million people.
A little lower, it says *adults*. And that would be around 70 milion.
Either way it's a big number but I suspect 70 million is closer to it. Allowing for overlap that would be 40 million or so of each.
Which sounds about right, no?
And a honking lot of potential ebook buyers.