public void mul(Fraction f) {
this.a = this.a * f.a;
this.b = this.b * f.b;
int gcd = Tool.gcd(this.a, this.b);
this.a = this.a / gcd;
this.b = this.b / gcd;
}
public void div(Fraction f) {
int tmp_a = this.a;
int tmp_b = this.b;
this.a = tmp_a * f.b;
this.b = tmp_b * f.a;
// System.out.println(this);
int gcd = Tool.gcd(this.a, this.b);
this.a = this.a / gcd;
this.b = this.b / gcd;
}