Prize Purses for Superfight

I found it odd that Bob Arum stated that Pac would only be receiving a 25 MILL guaranteed check the night of the fight plus a portion of backend revenue. In contrast, in the post fight press conference, Mayweather stated he received a check of approximately 100 million, not including his backend revenue(% of PPV, concessions, whatever) or endorsements(~ 25 mill for Burger King man, watch and whatever the hell else he was promoting) For a 60/40 split, using Mayweathers numbers, Pacquiao should have received a 66.66 Million check for the guaranteed. If Pac only got 25 Million, it almost seems like Arum pocketed 41.6 million dollars(62%) of Pacquaio's guaranteed purse. I can't understand why Bob would ever do such a thing...