C++ :

#include<cstdio>
#include<cstring>
#include<cmath>
#include<iostream>
#include<algorithm>
using namespace std;

int main()
{
    //freopen("input.txt","r",stdin);
    //freopen("output.txt","w",stdout);
    int t;
    cin>>t;
    while(t--)
    {
        int n,m;
        cin>>n>>m;
        cout<<(n*m)/5<<endl;
    }
    return 0;
}