#include <bits/stdc++.h>


using namespace std;
const int N = 1e7;
int main(){
	int n;
	double ans = 0,ans0 = 0;
	double arr[N],brr[N];
	cin>>n;
	for(int i = 0;i < n;i++){
		cin>>arr[i];
		ans += arr[i];
	}
	ans *= 3;
	for(int i = 0;i < n;i++){
		cin>>brr[i];
		ans0 += brr[i];
	}
	ans0 *= 2;
	double ann = 0;
	for(int i = 0;i < n;i++){
		ann += arr[i] - brr[i];
	}
	double a = ans - ans0;
	printf("%.6lf",a / ann);
	return 0;
} 

简直是无法理解

题号P5082