text: MathUtils = function() {};
   
  MathUtils.prototype.sum = function(number1, number2) {
          return number1 + number2;
  }
   
  MathUtils.prototype.substract = function(number1, number2) {
      return number1 - number2;
  }
   
  MathUtils.prototype.multiply = function(number1, number2) {
      return number1 * number2;
  }
   
  MathUtils.prototype.divide = function(number1, number2) {
      if (number2 === 0){
          throw new Error ('Division por cero no permitida');
      }
      return number1 / number2;
  }
   
  MathUtils.prototype.average = function(number1, number2) {
      return (number1 + number2) / 2;
  }
   
  MathUtils.prototype.factorial = function(number) {
      if (number < 0) {
          throw new Error("There is no factorial for negative numbers");
      } else if (number == 1 || number == 0) {
          return 1;
      } else {
          return number * this.factorial(number - 1);
      }
  }