//#include "testlib.h"
 
#include <iostream>
#include <stdio.h>
#include <math.h>
#include <map>
#include <vector>
#include <stdlib.h>
#include <memory.h>
#include <time.h>
#include <string>
#include <algorithm>
#include <set>
#include <stack>
#include <cassert>
#include <queue>
#include <numeric>
 
using namespace std;
 
int main() {
    ios::sync_with_stdio(0);
    int t;
    cin >> t;
    while (t --> 0) {
        int T1, T2, t1, t2;
        cin >> T1 >> T2 >> t1 >> t2;
        
        double SQ1, SQ2;
        if (T1 > T2) {
            swap(T1, T2);
            swap(t1, t2);
        }
        
        if (t1 > T2) t1 = T2;
        if (t2 > T1) t2 = T1;
        
        SQ1 = T1 * 0.5 * T1;
        if (T1 > t2)
            SQ1 -= (T1 - t2) * 0.5 * (T1 - t2);
        
        
        if (t1+T1 <= T2) {
            SQ2 = T1 * 1.0 * t1;
        }
        else {
            // t1+T1 >= T2
            SQ2 = T1 * 0.5 * T1;
            SQ2 += (T1) * 1.0 * (T2-T1);
            SQ2 -= (T2-t1) * 0.5 * (T2-t1);
        }
    
        cout.precision(6);
        cout << fixed << (SQ1 + SQ2) / (T1 * 1ll * T2) << "\n";
    }
    return 0;
}