Ruby Numeric class method for returning a letter grade as a string, takes any Numeric object, returns a string.

grade.rb

class Numeric
  def to_grade
    case self
    when 97..100; grade = 'A+'
    when 94..96; grade = 'A'
    when 90..93; grade = 'A-'
    when 87..89; grade = 'B+'
    when 84..86; grade = 'B'
    when 80..83; grade = 'B-'
    when 77..79; grade = 'C+'
    when 74..76; grade = 'C'
    when 70..73; grade = 'C-'
    when 67..69; grade = 'D+'
    when 64..66; grade = 'D'
    when 60..63; grade = 'D-'
    when 0..59; grade = 'F'
    else grade = 'N/A'
    end

    grade
  end
end