E

#include <bits/stdc++.h>

using namespace std;

#define _test   int _TEST; cin>>_TEST; while(_TEST--)

int main()
{
    _test
    {
        double b, m, n, k;
        cin>>b>>m>>n>>k;

        if(b == 1)
        {
            cout<<m<<"\n";
            continue;
        }

        double r = (m*1.0)/(m+n);

        cout<<fixed<<setprecision(10);

        if(k == b)  cout<<m+r*(k-1)<<"\n";
        else        cout<<m-r<<"\n";
    }
}