input: def evaluate_expression(expr: str) -> float:
      """Evaluates a given string containing a numerical expression and returns the result.
      >>> evaluate_expression("2 + 3 * 4")
      14.0
      >>> evaluate_expression("(2 + 3) * 4")
      20.0
      >>> evaluate_expression("10 / 2")
      5.0
      """
output:     return eval(expr)