uva 10491 概率

#include <bits/stdc++.h>using namespace std;int main(int argc, char const *argv[]){double a, b, c;while (cin >> a >> b >> c)printf("%.5f\n", b * (a + b - 1) / (a + b) / (a + b - c - 1));return 0;}

照书上分析就好