//*
#define _CRT_SECURE_NO_WARNINGS
#include<stdio.h>
#include<algorithm>
#include<vector>
#define all(A) (A).begin(), (A).end()
using namespace std;
typedef long long ll;
typedef pair<int,int> pii;
const int MN = 5000+1;
const ll mod = 1000000007;
int N;
ll p[MN],d[MN];
ll mpow(ll a,ll p){
ll r=1;
while(p>0){
if(p&1)r=r*a%mod;
a=a*a%mod;
p>>=1;
}
return r;
}
ll inverse(ll a){
return mpow(a,mod-2);
}
const ll ti = inverse(1000000000);
ll D[MN][MN];
ll A[MN][MN];
ll fact[MN];
int main(){
scanf("%d",&N);
fact[0]=1;
for(int i=1;i<=N;i++)fact[i]=fact[i-1]*i%mod;
for(int i=0;i<N;i++){
scanf("%lld%lld",&p[i],&d[i]);
p[i]=p[i]*ti%mod;
d[i]=d[i]*p[i]%mod;
}
D[0][0]=1;
D[0][1]=1-p[0];
for(int i=1;i<N;i++){
D[i][0]=1;
for(int j=1;j<=i+1;j++){
D[i][j]=(1-p[i])*D[i-1][j-1]+D[i-1][j];
D[i][j]%=mod;
}
}
for(int i=0;i<N;i++){
A[i][0]=1;
for(int j=1;j<N;j++){
A[i][j]=D[N-1][j]-(1-p[i])*A[i][j-1];
A[i][j]%=mod;
}
}
ll ans=0;
for(int i=0;i<N;i++)for(int j=0;j<N;j++){
ans+=d[i]*fact[j]%mod*fact[N-j-1]%mod*A[i][j]%mod;
ans%=mod;
}
if(ans<0)ans+=mod;
ans=ans*inverse(fact[N])%mod;
printf("%lld\n",ans);
return 0;
}
//*/
