1 //STATUS:C++_AC_281MS_1440KB
  2 #include <functional>
  3 #include <algorithm>
  4 #include <iostream>
  5 //#include <ext/rope>
  6 #include <fstream>
  7 #include <sstream>
  8 #include <iomanip>
  9 #include <numeric>
 10 #include <cstring>
 11 #include <cassert>
 12 #include <cstdio>
 13 #include <string>
 14 #include <vector>
 15 #include <bitset>
 16 #include <queue>
 17 #include <stack>
 18 #include <cmath>
 19 #include <ctime>
 20 #include <list>
 21 #include <set>
 22 #include <map>
 23 using namespace std;
 24 //#pragma comment(linker,"/STACK:102400000,102400000")
 25 //using namespace __gnu_cxx;
 26 //define
 27 #define pii pair<int,int>
 28 #define mem(a,b) memset(a,b,sizeof(a))
 29 #define lson l,mid,rt<<1
 30 #define rson mid+1,r,rt<<1|1
 31 #define PI acos(-1.0)
 32 //typedef
 33 typedef __int64 LL;
 34 typedef unsigned __int64 ULL;
 35 //const
 36 const int N=10010;
 37 const int INF=0x3f3f3f3f;
 38 const int MOD=10007,STA=8000010;
 39 const LL LNF=1LL<<55;
 40 const double EPS=1e-9;
 41 const double OO=1e30;
 42 const int dx[4]={-1,0,1,0};
 43 const int dy[4]={0,1,0,-1};
 44 const int day[13]={0,31,28,31,30,31,30,31,31,30,31,30,31};
 45 //Daily Use ...
 46 inline int sign(double x){return (x>EPS)-(x<-EPS);}
 47 template<class T> T gcd(T a,T b){return b?gcd(b,a%b):a;}
 48 template<class T> T lcm(T a,T b){return a/gcd(a,b)*b;}
 49 template<class T> inline T lcm(T a,T b,T d){return a/d*b;}
 50 template<class T> inline T Min(T a,T b){return a<b?a:b;}
 51 template<class T> inline T Max(T a,T b){return a>b?a:b;}
 52 template<class T> inline T Min(T a,T b,T c){return min(min(a, b),c);}
 53 template<class T> inline T Max(T a,T b,T c){return max(max(a, b),c);}
 54 template<class T> inline T Min(T a,T b,T c,T d){return min(min(a, b),min(c,d));}
 55 template<class T> inline T Max(T a,T b,T c,T d){return max(max(a, b),max(c,d));}
 56 //End
 57
 58 vector<int> q[N];
 59 double k[N],e[N],A[N],B[N],C[N];
 60 int T,n;
 61
 62 void dfs(int u,int fa)
 63 {
 64     int i,j,v,m=q[u].size();
 65     double P=(1-k[u]-e[u])/(m);
 66     double At,Bt,Ct;
 67     At=Bt=Ct=0;
 68     for(i=0;i<m;i++){
 69         v=q[u][i];
 70         if(v==fa)continue;
 71         dfs(v,u);
 72         At+=A[v];
 73         Bt+=B[v];
 74         Ct+=C[v];
 75     }
 76     A[u]=(P*At+k[u])/(1-P*Bt);
 77     B[u]=P/(1-P*Bt);
 78     C[u]=(P*Ct+1-k[u]-e[u])/(1-P*Bt);
 79 }
 80
 81 int main(){
 82  //   freopen("in.txt","r",stdin);
 83     int ca=1,i,j,a,b;
 84     scanf("%d",&T);
 85     while(T--)
 86     {
 87         scanf("%d",&n);
 88         for(i=1;i<=n;i++)q[i].clear();
 89         for(i=1;i<n;i++){
 90             scanf("%d%d",&a,&b);
 91             q[a].push_back(b);
 92             q[b].push_back(a);
 93         }
 94         for(i=1;i<=n;i++){
 95             scanf("%lf%lf",&k[i],&e[i]);
 96             k[i]/=100,e[i]/=100;
 97         }
 98
 99         dfs(1,0);
100
101         printf("Case %d: ",ca++);
102         if(sign(A[1]-1))printf("%.6lf\n",C[1]/(1-A[1]));
103         else printf("impossible\n");
104     }
105     return 0;
106 }