coffee.rb

# Now more objecty

class PotOfCoffee
  attr_reader :scoops

  def initialize(quantity: 12, strength: :normal)
    @quantity = quantity
    @strength = strength
  end

  def ratio
    @ratio = { weak: 0.5, normal: 0.75, extra: 0.875, turbo: 1, omg: 2, wtf: 3.8 }
  end

  def scoops
    quantity * ratio.fetch(strength)
  rescue KeyError
    "I don't know how to make #{strength} strength coffee, sorry."
  end

end

pot = PotOfCoffee.new
puts pot.scoops # 9.0

extra_pot = PotOfCoffee.new(quantity: 8, strength: :extra)
puts extra_pot.scoops # 7.0

wtf_pot = PotOfCoffee.new(quantity: 12, strength: :wtf)
puts wtf_pot.scoops # 45.599999999999994

error_pot = PotOfCoffee.new(quantity: 12, strength: 'asdgas')
puts error_pot.scoops # "I don't know how to make asdgas strength coffee, sorry."

I think you're too tightly coupling the concept of a Scoop and a Pot. They are clearly different objects with different behaviors.