1 #include<cstdio>
 2 #include<algorithm>
 3 #include<cstring>
 4 #include<cmath>
 5 #include<iostream>
 6 #include<cctype>
 7 #include<set>
 8 #include<vector>
 9 #include<queue>
10 #include<map>
11 using namespace std;
12 typedef long long LL;
13
14 inline int read() {
15     int x=0,f=1;char ch=getchar();for(;!isdigit(ch);ch=getchar())if(ch=='-')f=-1;
16     for(;isdigit(ch);ch=getchar())x=x*10+ch-'0';return x*f;
17 }
18
19 const int N = 10010;
20 const double eps =  1e-10;
21
22 double A[N], B[N], C[N], k[N], e[N];
23 vector<int> T[N];
24
25 bool dfs(int u,int fa) {
26     double m = 1.0 * T[u].size();
27     A[u] = k[u], B[u] = (1 - k[u] - e[u]) / m, C[u] = 1 - k[u] - e[u];
28     double t = 0;
29     for (int i=0; i<m; ++i) {
30         int v = T[u][i];
31         if (v == fa) continue;
32         if (!dfs(v, u)) return false;
33         A[u] += (1 - k[u] - e[u]) / m * A[v];
34         C[u] += (1 - k[u] - e[u]) / m * C[v];
35         t += (1 - k[u] - e[u]) / m * B[v];
36     }
37     if (fabs(1 - t) <= eps) return false;
38     A[u] /= (1 - t), B[u] /= (1 - t), C[u] /= (1 - t);
39     return true;
40 }
41
42 int main() {
43     for (int Case=read(),t=1; t<=Case; ++t) {
44         int n = read();
45         for (int i=1; i<=n; ++i) T[i].clear();
46         for (int i=1; i<n; ++i) {
47             int u = read(), v = read();
48             T[u].push_back(v), T[v].push_back(u);
49         }
50         for (int i=1; i<=n; ++i) {
51             int a = read(), v = read();
52             k[i] = (double)a / 100.0;
53             e[i] = (double)v / 100.0;
54         }
55         printf("Case %d: ",t);
56         if (dfs(1, 0) && fabs(A[1] - 1) > eps)
57             printf("%.10lf\n",C[1] / (1 - A[1]));
58         else puts("impossible");
59     }
60     return 0;
61 }