1 #include <cstdio>
 2 #include <algorithm>
 3 #include <iostream>
 4 #include <cstring>
 5 #include <string>
 6 #include <cmath>
 7 #include <queue>
 8 #include <vector>
 9 using namespace std;
10 #define N 10010
11 const double eps = 1e-9;
12 
13 double k[N], e[N];
14 double A[N], B[N], C[N];
15 vector<int> G[N];
16 
17 bool dfs(int u, int pre)
18 {
19     int l = G[u].size();
20     A[u] = k[u];
21     B[u] = (1 - k[u] - e[u]) / l;
22     C[u] = 1 - k[u] - e[u];
23     double tmp = 0;
24     for(int i = 0; i < l; i++) {
25         int v = G[u][i];
26         if(v == pre) continue;
27         if(!dfs(v, u)) return false;
28         A[u] += (1 - k[u] - e[u]) * A[v] / l;
29         C[u] += (1 - k[u] - e[u]) * C[v] / l;
30         tmp += (1 - k[u] - e[u]) * B[v] / l ;
31     }
32     if(fabs(tmp - 1) < eps) return false;
33     A[u] /= (1 - tmp);
34     B[u] /= (1 - tmp);
35     C[u] /= (1 - tmp);
36     return true;
37 }
38 
39 int main()
40 {
41     int t, cas = 1;
42     scanf("%d", &t);
43     while(t--) {
44         memset(A, 0, sizeof(A));
45         memset(B, 0, sizeof(B));
46         memset(C, 0, sizeof(C));
47         int n;
48         scanf("%d", &n);
49         for(int i = 0; i <= n; i++)
50             G[i].clear();
51         for(int i = 1; i < n; i++) {
52             int u, v;
53             scanf("%d%d", &u, &v);
54             G[u].push_back(v);
55             G[v].push_back(u);
56         }
57         for(int i = 1; i <= n; i++) {
58            scanf("%lf%lf", &k[i], &e[i]);
59            k[i] /= 100; e[i] /= 100;
60         }
61         printf("Case %d: ", cas++);
62         if(dfs(1, -1) && fabs(A[1] - 1) > eps) {
63             printf("%.6f\n",  C[1] / (1 - A[1]));
64         } else {
65             puts("impossible");
66         }
67     }
68 
69     return 0;
70 }