A Note on the Ratio of Revenues Between Selling in a Bundle and   Separately
  We consider the problem of maximizing revenue when selling k items to a single buyer with known valuation distributions. We show that for a single, additive buyer whose valuations for for the items are distributed according to i.i.d. distributions which are known to the seller, the ratio of revenue from selling in a bundle to selling separately is at least 55.9% and this gap is attainable. 
Ron Kupfer
cs.GT