public void sum(Div other){
			if(b == other.b){
				a = a.add(other.a);
			}else{
				a = a.multiply(other.b).add(b.multiply(other.a));
				//a = a*other.b + b*other.a;
				b = b.multiply(other.b);
				//b = b*other.b;
			}
			
			BigInteger red = reduce(a,b);
			a = a.divide(red);
			b = b.divide(red);
		}