#include <bits/stdc++.h>
//#include <atcoder/all>
using namespace std;
// using namespace atcoder;
// using mint = modint1000000007;
// const int mod = 1000000007;
// using mint = modint998244353;
// const int mod = 998244353;
// const int INF = 1e9;
// const long long LINF = 1e18;
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define rep2(i, l, r) for (int i = (l); i < (r); ++i)
#define rrep(i, n) for (int i = (n)-1; i >= 0; --i)
#define rrep2(i, l, r) for (int i = (r)-1; i >= (l); --i)
#define all(x) (x).begin(), (x).end()
#define allR(x) (x).rbegin(), (x).rend()
#define P pair<int, int>
template<typename A, typename B> inline bool chmax(A &a, const B &b) { if (a < b) { a = b; return true; } return false; }
template<typename A, typename B> inline bool chmin(A &a, const B &b) { if (a > b) { a = b; return true; } return false; }
void test() {
	rep2(n, 2, 100)rep2(m, 1, 100)rep2(k, 1, n*m) {
		double ans = 0;
		{
			long long x = (k + m - 1) / m;
			ans += (double)(n - x) / n;
		}
		{
			long long x = (k + m) / m;
			double tmp = (double)x / n;
			tmp -= ans;
			tmp *= ((double)m - 1) / m;
			ans += tmp;
		}
		if (ans > 1.0) {
			cout << n << " " << m << " " << k << endl;
			cout << fixed << setprecision(16);
			cout << ans << endl;
			return;
		}
	}
	cout << "comprete" << endl;
	//	cout << ans << endl;
}
int main() {
	std::ios::sync_with_stdio(false);
	std::cin.tie(nullptr);
	//test(); return 0;
	int t; cin >> t;
	cout << fixed << setprecision(16);
	while (t--) {
		long long n, m, k; cin >> n >> m >> k;
		double ans = 0;
		{// 00000000
			long long x = (k + m - 1) / m;
			ans += (double)(n - x) / n;
		}
		{// 000000010
			long long x = (k + m) / m;
			double tmp = (double)x / n;
			tmp -= ans;
			tmp *= ((double)m - 1) / m;
			ans += tmp;
		}
		if (ans > 1.0)return -1;
		cout << ans << endl;

	}
	return 0;
}