second_solution.rb

value_matrix = { "zero" => 0, 
                 "one" => 1,
                 "two" => 2,
                 "three" => 3,
                 "four" => 4,
                 "five" => 5,
                 "six" => 6,
                 "seven" => 7,
                 "eight" => 8,
                 "nine" => 9 }

value_matrix.each do |key, value|
  define_method(key.to_sym) do |method = nil|
    calculate(method, value)
  end
end

symbol_matrix = { "plus" => "+",
                  "minus" => "-",
                  "times" => "*",
                  "divided_by" => "/" }
                  
symbol_matrix.each do |key, value|
  define_method(key.to_sym) do |amount|
    "#{value} #{amount}.to_f"
  end
end

def calculate(method, value)
  method ? eval("#{value} #{method}") : value
end