1 #include<cstdio>
 2 #include<cstring>
 3 #include<iostream>
 4 #include<cmath>
 5 #include<algorithm>
 6 const double eps=1e-9;
 7 int tot,go[500005],first[500005],next[500005];
 8 double a[500005],b[500005],c[500005],k[500005],e[500005];
 9 int n,du[500005];
10 void insert(int x,int y){tot++;go[tot]=y;next[tot]=first[x];first[x]=tot;}
11 void add(int x,int y){insert(x,y);insert(y,x);}
12 bool dfs(int x,int fa){
13     bool Isleave=1;
14     double tmp=0;
15     a[x]=k[x];
16     b[x]=c[x]=(1-k[x]-e[x]);
17     b[x]/=du[x];
18     for (int i=first[x];i;i=next[i]){
19         int pur=go[i];
20         if (pur==fa) continue;
21         Isleave=0;
22         if (!dfs(pur,x)) return false;
23         a[x]+=a[pur]*(1-k[x]-e[x])/du[x];
24         c[x]+=c[pur]*(1-k[x]-e[x])/du[x];
25         tmp+=(b[pur])*(1-k[x]-e[x])/du[x];
26     }
27     if (fabs(tmp-1)<=eps) return false;
28     a[x]/=(1-tmp);
29     b[x]/=(1-tmp);
30     c[x]/=(1-tmp);
31     return true;
32 }
33 int main(){
34     int T,Tcase=0;
35     scanf("%d",&T);
36     while (T--){
37         Tcase++;
38         tot=0;
39         memset(first,0,sizeof first);
40         memset(du,0,sizeof du);
41         scanf("%d",&n);
42         for (int i=1;i<n;i++){
43             int x,y;
44             scanf("%d%d",&x,&y);
45             add(x,y);
46             du[x]++;
47             du[y]++;
48         }
49         for (int i=1;i<=n;i++){
50             scanf("%lf%lf",&k[i],&e[i]);
51             k[i]/=100;e[i]/=100;
52         }
53         printf("Case %d: ",Tcase);
54         if (dfs(1,0)&&fabs(1-a[1])>eps){
55             printf("%.6f\n",c[1]/(1-a[1]));
56         }
57         else{
58             printf("impossible\n");
59         }
60     }
61 }