The Answer to Derek's Pizza Party

Answers:

46 + 25 = 71 (This is how many friends that ate pepperoni pizza.)
35 + 25 = 60 (This is how many friends that ate cheese pizza.)
125 - 19 = 46 + 35 + 25 = 106 (This is how many friends that ate pizza altogether.)
125 - 71 = 35 + 19 = 54 (This is how many friends that didn't eat pepperoni pizza.)
46 + 35 + 25 + 19 = 125 (This is how many friends that came to Derek's party.)

Isn't Derek popular? He invited so many friends!