I Haven't Seen This Thread Anywhere So I'm Assuming It Hasn't Been Posted!
Steps:
1. Get DeadSilence Pro ( x Amount of Kills In close Range using Dead Silence )
2. Find a Hill Or A Ledge you Can Jump Off ( Doesn't Have To Be High, Just Enough That You Should Get Fall Damage )
3. Jump Off And Repeat Step 2. It Takes 20 Jumps For a 10,000 XP Challenge.