Marbles

                            Solution in C :

#include <stdio.h>
int main()
{
	int t;
	scanf("%d",&t);
	while(t--)
	{
		long long int n,k;scanf("%lld %lld",&n,&k);
		long long int d=n-k,sum=1;
		if(n==k) {
		sum=1;
		}
		else
		{
			for(long long int i=1;i<k;i++)
			{
				sum=sum*(d+i);
				sum=sum/i;
			}
		}
		printf("%lld\n",sum);
	}
	return 0;
}
                        

                        Solution in C++ :

#include<bits/stdc++.h>
using namespace std;

#define ll long long 
#define  ld long double 
#define vl vector<ll> 
#define vi vector<int> 
#define vs vector<string> 
#define vvl vector<vl> 
#define vvvl vector<vvl> 
#define  vvs vector<vs> 
#define   vvi vector<vi> 
#define  vs vector<string> 
#define  vvs vector<vs>
using namespace std;


ll comb(ll n, ll k){
    ll ans = 1;
    if (2*k > n) k = n-k;

    for(ll i=1; i<=k; i++){
        ans *= n;
        ans /= i;
        n--;
    }

    return ans;
}

void solve(){
    ll n,k; cin>>n>>k;

    cout << comb(n-1, k-1) << endl;
}


int main(){
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    ll t; 
    cin>>t;
   while(t--)
        solve();
    
    return 0;
}
                    

                        Solution in Java :

/* package codechef; // don't place package name! */

import java.util.*;
import java.lang.*;
import java.io.*;

/* Name of the class has to be "Main" only if the class is public. */
class Codechef
{
    public static long fact(int n)
    {
        long res=0;
        if(n==1||n==0)
        {
            res= 1;
        }
        else{
            res =  n*fact(n-1);
        }
        return res;
    }
	public static void main (String[] args) throws java.lang.Exception
	{
		// your code goes here
		int n,k,t;
		long poss;
		Scanner sc = new Scanner(System.in);
		t = sc.nextInt();
		while(t>0)
		{
		    t--;
		    n = sc.nextInt();
		    k = sc.nextInt();
		    if(n==k)
		    {
		        poss =1;
		    }
		    else 
		    {
		        int m = n-k; poss = 1;
		        for(int i=1;i<k;i++)
		        {
		            poss = poss*(m+i)/i;
		        }
		    }
		    System.out.println(poss);
		}
	}
}
                    

                        Solution in Python : 
                            
n=int(input())
for i in range(n):
    n,b=map(int,input().split())
    r1=1
    for i in range(1,b):
        r1=r1*(n-b+i)//(i)
    print(int(r1))