function check(df)
{
	var x=df.value;
	if(isNaN(x))
	{
		var a=x.substring(0,(x.length-1))
		df.value=a;
	}
}	


function pc()
{
	var n=parseInt(document.per.p1.value);
	var r=parseInt(document.per.p2.value);
	if(r>n)
	{
		alert("Number of sample points r should be less than Number of sample points in set n");
	}
	else
	{
//n!
		var z=1;
		for(var i=n;i>=1;i--)
		{
			z=z*i;
		}

//r!
		var x=1;
		for(var k=r;k>=1;k--)
		{
			x=x*k;
		}

//(n-r)!
		var s=n-r;
		var t=1;
		for(var j=s;j>=1;j--)
		{
			t=t*j;
		}	

//PERMUTATION [ n!/(n-r)! ]
		var p=z/t;
		document.per.p3.value=Math.round((p)*1000)/1000;

//COMBINATION [ (n!/(n-r)!) / r! ]
		var c=p/x;
		document.per.p4.value=Math.round((c)*1000)/1000;
	}
}