1 #include <cstdio>
2 #include <cstring>
3 #include <algorithm>
4 #include <iostream>
5 #include <vector>
6 #include <cmath>
7
8 using namespace std;
9 const int maxn=10000+100;
10 int T,n;
11 double E[maxn],K[maxn],A[maxn],B[maxn],C[maxn];
12 vector<int>G[maxn];
13 bool dfs(int u,int fa){
14 double temp=0;
15 if(G[u].size()==1&&fa!=-1){
16 A[u]=K[u];
17 B[u]=1-K[u]-E[u];
18 C[u]=1-K[u]-E[u];
19 return true;
20 }
21 A[u]=K[u];
22 B[u]=(1-K[u]-E[u])/G[u].size();
23 C[u]=1-K[u]-E[u];
24 for(int i=0;i<G[u].size();i++){
25 int v=G[u][i];
26 if(v!=fa){
27 if(!dfs(v,u))return false;
28 A[u]+=A[v]*(1-K[u]-E[u])/G[u].size();
29 C[u]+=(1-K[u]-E[u])/G[u].size()*C[v];
30 temp+=B[v]*(1-K[u]-E[u])/G[u].size();
31 }
32 }
33 if(fabs(1-temp)<=1e-10)return false;
34 A[u]/=(1-temp);
35 B[u]/=(1-temp);
36 C[u]/=(1-temp);
37 return true;
38 }
39 int main(){
40 scanf("%d",&T);
41 for(int t=1;t<=T;t++){
42 memset(A,0,sizeof(A));
43 memset(B,0,sizeof(B));
44 memset(C,0,sizeof(C));
45 scanf("%d",&n);
46 for(int i=1;i<=n;i++)G[i].clear();
47 int x,y;
48 for(int i=1;i<n;i++){
49 scanf("%d%d",&x,&y);
50 G[x].push_back(y);
51 G[y].push_back(x);
52 }
53 for(int i=1;i<=n;i++){
54 scanf("%lf%lf",&K[i],&E[i]);
55 K[i]/=100,E[i]/=100;
56 }
57 printf("Case %d: ",t);
58 if(!dfs(1,-1)||(1-A[1])<=1e-10){
59 printf("impossible\n");
60 continue;
61 }
62 /* for(int i=1;i<=n;i++){
63 cout<<i<<" "<<C[i]<<endl;
64 }*/
65 printf("%.6f\n",C[1]/(1-A[1]));
66 }
67 return 0;
68 }
