#include <iostream>
#include<cstdio>
#include<algorithm>
#include <cmath>
using namespace std;
//const int N=1e8+5;
//void initialise(int n)
//{
//
//}
int main()
{
	int t;
	double H,h,D;
	scanf("%d",&t);
	while(t--)
	{
		scanf("%lf%lf%lf",&H,&h,&D);
//        initialise(n);
		double add=D/2-(H-h);
		if(add>0)
		{
			printf("%.3lf\n",h+add);
		}
		else
		{
			printf("%.3lf\n",h);
		}
	}
	return 0;
}