Mary wants to bake 10 apple pies for a charity event. Each pie needs 8 apples and she already harvested 50 apples from the trees in her garden. How many more apples does she need to buy to make all 10 pies?
She needs 10*8=<<10*8=80>>80 apples to make the pies
So she has to buy 80-50=<<80-50=30>>30 more apples
#### 30