#include <bits/stdc++.h>

 #define LL long long

 using namespace std;

 inline int ra()

 {

     int x=,f=; char ch=getchar();

     while (ch<'' || ch>'') {if (ch=='-') f=-; ch=getchar();}

     while (ch>='' && ch<='') {x=x*+ch-''; ch=getchar();}

     return x*f;

 }

 LL n,m,cnt=;

 double ans,tot;

 struct edge{

     int from,to,next;

     LL v,T;

 }e[];

 LL size[],head[],deep[];

 void insert(int x, int y, int v)

 {

     e[++cnt].next=head[x]; e[cnt].from=x; e[cnt].to=y; e[cnt].v=v; head[x]=cnt;

 }

 void dfs(int x, int fa)

 {

     size[x]=;

     for (int i=head[x];i;i=e[i].next)

     {

         if (e[i].to==fa) continue;

         deep[e[i].to]=deep[x]+;

         dfs(e[i].to,x);

         size[x]+=size[e[i].to];

     }

 }

 int main(int argc, char const *argv[])

 {

     n=ra(); tot=n*(n-)*(n-)/6.0;

     for (int i=; i<n; i++)

     {

         int x=ra(),y=ra(),v=ra();

         insert(x,y,v); insert(y,x,v);

     }

     dfs(,);

     for (int i=; i<=cnt; i+=)

     {

         int now=i/,x=e[i].from,y=e[i].to;

         if (deep[x]>deep[y]) swap(x,y);

         LL s1=n-size[y],s2=size[y];

         e[i].T+=s1*s2*((LL)n-);

         ans+=e[i].T*e[i].v;

     }

     m=ra();

     for (int i=; i<=m; i++)

     {

         int x=ra(),y=ra();

         LL now=x*;

         ans-=(e[now].v-y)*e[now].T;

         e[now].v=y;

         printf("%.10lf\n",(double)ans/tot);

     }

     return ;

 }