public void add(Fraction other){
        int otherNum = other.getNumerator();
        int otherDen = other.getDenominator();
        int commonDen = otherDen * denominator;
        numerator = numerator*otherDen + otherNum*denominator;
        denominator = commonDen;
    }

    public void subtract(Fraction other){
        if( denominator != other.getDenominator()){
            numerator = numerator * other.getDenominator();
            int otherNum = other.getNumerator() * denominator;
            numerator = numerator - otherNum;
            denominator = denominator * other.getDenominator();
        }
        else
            numerator = numerator - other.getNumerator();
    }

    public void multiply(Fraction other){
        numerator = numerator * other.getNumerator();
        denominator = denominator * other.getDenominator();
    }