I love your feet Ryan

gistfile1.rb

GRADES = ['A', 'B', 'C', 'D']

def grade_formula(book_count, reads_books = true)
   raise "One cannot have read a negative amount of books, you numbnuts." if book_count < 0

   index = case book_count
   when 0..9
     3
   when 10..20
     2
   else
     1
   end

   index -= 1 if reads_books

   GRADES[index]
end