Help with Drop chance, modified arena

[BabaVoss]

-	script	1	-1,{
	OnNPCKillEvent:
		if ( getmonsterinfo( killedrid, 21 ) ) {
			if(killedrid == (2927)){
				getitem 6319,1; //item 
			}
			if(killedrid == (2750)){
				getitem 6319,1; //item 
			}
			if(killedrid == (2049)){
				getitem 6224,1; //item 
			}

			if(killedrid == (3088)){
				getitem 6224,1; //item 
			}

			if(killedrid == (2250)){
				getitem 6090,1; //item 
			}

			if(killedrid == (2951)){
				getitem 6090,1; //item
			}

			}
	end;
}

Hello guys good day, can anyone help with this script. I made this script as a modified arena. I need it to be drop by chance only. sorry still a newbie. thanks in advance

[EveeX]

Use rand( ) function to add a chance

[Emistry]

if (rand(100) < 10)
	getitem 512, 100; // 10%