Irreducible Fraction

[Claws]

I need to do class inheritance. There are 3 classes: Base class Pair, and 2 derived clases from Pair :Rational and Complex.
I have no question about class Complex, so I will post code only for class Pair and Rational.
Class Pair must contain 2 real type data members, as you see I named them "double a" and "double b". In class Rational, "a=numerator" and "b=denominator".
In class Complex, "a=real" and "b=imaginary"
Base class Pair also contains operator <<.
Each class , Rational and Complex must contain:
*constructor;
*operator+;
*operator*;

My question is about Rational class. For example if I put 3/10 + 1/5, result must be 1/2, and I have no ideea how to do that, I'm beginner and I also lost 10 h browsing the internet about how to solve this, but I can't make it. If anyone of you can give me some hints about how to solve this, I will really appreciate :)
Also, I will put here main code, and it must remain untouched.
Code contain: main.cpp, Pair.h, Pair.cpp, Rational.h, Rational.cpp

>>>.................main.cpp......................<<<

#include <iostream>
#include "Pair.h"
#include "Rational.h"
#include "Complex.h"

using namespace std;

int main()
 {
    Rational r1(3,10), r2(1,5);
    cout << "Rational: " << r1 <<" + "<< r2<<" = "<<r1+r2<< endl;
    cout << "Rational: " << r1 <<" * "<< r2<<" = "<<r1*r2<< endl;
   // Complex c1(3, 10), c2(1, 5);
   // cout << "Complex: " << c1 <<" + "<< c2<<" = "<<c1+c2<< endl;
   // cout << "Complex: " << c1 <<" * "<< c2<<" = "<<c1*c2<< endl;
 //cout << "Complex: " << c1 + c2 << endl;
 //cout << "Complex: " << c1 * c2 << endl;
 return 0;
 }

>>>.......................Pair.h......................<<<

  #ifndef PAIR_H
#define PAIR_H
#include<iostream>
using namespace std;


class Pair
{
    friend ostream& operator<<(ostream&, const Pair&);
    public:
        Pair();
        virtual ~Pair();
    protected:
        double a;
        double b;
    private:
};

#endif // PAIR_H


>>>.................Pair.cpp...................<<<

#include "Pair.h"

Pair::Pair()
{
    //ctor
}

ostream& operator<<(ostream& out, const Pair& val)
{
    out<<"("<<val.a<<","<<val.b<<")";
    return out;
}

Pair::~Pair()
{
    //dtor
}

>>>......................Rational.h.........................<<<

#ifndef RATIONAL_H
#define RATIONAL_H
#include "Pereche.h"

class Rational: public Pair
{
    public:
        Rational(double=0,double=1);
       Rational operator+(const Rational&);
       Rational operator*(const Rational&);
      //friend Rational operator+(const Rational, const Rational);
      // friend Rational operator*(const Rational, const Rational);
         int fractie(int , int);
        virtual ~Rational();
    protected:
    private:

#endif // RATIONAL_H

>>>..................Rational.cpp................<<<

#include "Rational.h"

Rational::Rational(double numerator, double denominator)
{
    a=numerator;
    b=denominator;
}

Rational Rational::operator+(const Rational& r)
{
    return Rational(this->a + r.a, this->b + r.b);
}

Rational Rational::operator*(const Rational& r)
{
    return Rational(this->a * r.a,this->b * r.b);
}

Rational::~Rational()
{
    //dtor
}