#include <iostream>
#include <cmath>
using namespace std;
int n, h;
double s;
int main()
{
	cin >> n;
	while (cin >> h >> n)
	{
		s = h;
		while (--n) s += pow(0.5, n - 1) * h;
		printf("%.2f\n", s);
	}
	return 0;
}