def cached_amount(original, target, amount)
      if rate = cached_rate(original, target)
        result = (amount * rate).to_f
        return result = (result * 100).round.to_f / 100
      end
      nil
    end
def cached_amount(original, target, amount)
      if rate = cached_rate(original, target)
        result = (amount * rate).to_f
        return result = (result * 100).round.to_f / 100
      end
      nil
    end
Checks if there's a cached rate and calculates the result
 from the amount (or returns nil).