题目链接:https://ac.nowcoder.com/acm/contest/697/A
题目大意:
大佬博客:https://www.cnblogs.com/tweetuzki/p/10777822.html
代码:
#include<bits/stdc++.h>
#define ll long long
using namespace std;
const ll MOD=1e9+7;
ll quick_pow(ll a,ll b,ll c)
{
ll ans=1;
while(b>0)
{
if(b%2==1) ans=ans*a%c;
a=a*a%c;
b/=2;
}
return ans;
}
int main()
{
int ans=0,n,a,b;
cin>>n;
for(int i=1;i<=n;i++)
{
cin>>a>>b;
ans=(ans+1)*b%MOD*quick_pow(a,MOD-2,MOD)%MOD;
}
cout<<ans<<endl;
}