Greta the goose eats 20/10=<<20/10=2>>2 pounds of food per day.
Milton the mouse eats (1/100)*2=1/50 of a pound of food per day.
Elmer the elephant eats 4000*(1/50)=<<4000*(1/50)=80>>80 pounds of food per day.
Thus, Elmer eats 80-20=60 pounds more food per day than does Penelope the pig.
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