/*************************************************************************
    > File Name: hdu4035.cpp
    > Author: ALex
    > Mail: 405045132@qq.com 
    > Created Time: 2014年12月21日 星期日 17时19分33秒
 ************************************************************************/

#include <map>
#include <set>
#include <queue>
#include <stack>
#include <vector>
#include <cmath>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <iostream>
#include <algorithm>
using namespace std;

const int N = 10010;
const double eps = 1e-9;
int  n;
double k[N], e[N];
double A[N], B[N], C[N];
vector <int> edge[N];

bool dfs(int u, int fa)
{
	int m = edge[u].size();
	A[u] = m *  k[u];
	B[u] = (1 - k[u] - e[u]);
	C[u] = m * (1 - k[u] - e[u]);
	double f = m;
	for (int i = 0; i < m; ++i)
	{
		int v = edge[u][i];
		if (v == fa)
		{
			continue;
		}
		if (!dfs(v, u))
		{
			return false;
		}
		A[u] += (1 - k[u] - e[u]) * A[v];
		C[u] += (1 - k[u] - e[u])  * C[v];
		f -= (1 - k[u] - e[u]) * B[v];
	}
	if (abs(f) <= eps)
	{
		return false;
	}
	A[u] /= f;
	B[u] /= f;
	C[u] /= f;
	return true;
}

int main()
{
	int t;
	int u, v;
	scanf("%d", &t);
	int icase = 1;
	while (t--)
	{
		memset (A, 0, sizeof(A));
		memset (B, 0, sizeof(B));
		memset (C, 0, sizeof(C));
		scanf("%d", &n);
		for (int i = 1; i <= n; ++i)
		{
			edge[i].clear();
		}
		for (int i = 1; i <= n - 1; ++i)
		{
			scanf("%d%d", &u, &v);
			edge[u].push_back(v);
			edge[v].push_back(u);
		}
		for (int i = 1; i <= n; ++i)
		{
			scanf("%lf%lf", &k[i], &e[i]);
			k[i] /= 100;
			e[i] /= 100;
		}
		printf("Case %d: ", icase++);
		if (!dfs(1, -1) || abs(A[1] - 1) <= eps)
		{
			printf("impossible\n");
		}
		else
		{
			printf("%.6f\n", C[1] / (1 - A[1]));
		}
	}
	return 0;
}