OMG GUIZE I FOUNDZ A UNIQUE MACHETE EXDEE

(The Last Stand: Dead Zone)

Sale 1

http://www.tf2outpost.com/trade/26792651 Sold for 13 keys

B/O for Pith was 13

X = 13

Some of the keys https://gyazo.com/9df991eadfa431502100468506329cf3 http://backpack.tf/profiles/76561198071995540?time=1439708400&compare=1439794800

Pith https://backpack.tf/item/1642722539

Just like the Blizz Napper's suggestion, some of the keys appear to have never entered the backpack, but a Strange Pro Killstreak Beggar's Bazooka entered the backpack on the same day https://backpack.tf/item/2698684847 It had a B/O of 5 keys though, but the offer made it clear it was 13

Sale 2

http://www.tf2outpost.com/trade/26974915 Sold with a Spec KS Original for 13 keys

B/O for Pith was 13

X + 1 = 13

X = 12

Original https://backpack.tf/item/2810845994

Pith https://backpack.tf/item/681793873

Keys https://gyazo.com/9154f1a3039c9dd592e38f98cf583023 http://backpack.tf/profiles/76561198128628781?time=1441954800&compare=1442127600

3 of the keys shown in the screenshot will not come up if you use the ID search, but the IDs of those 3 keys to the other 10 are within 100 of eachother, meaning they were also included

Sale 3

Sold for Pro KS S. Rocket Launcher + Pro KS S. Shotgun + a key

I don't even have to use math to know this is an outlier

Rocket https://backpack.tf/item/2490685936

Shotty https://backpack.tf/item/1808099164

Pith https://backpack.tf/item/506610919

Sale 4

http://www.tf2outpost.com/trade/27048597 Sold for 12 keys + S. KS Carbanado Knife

B/O for Pith was 13

X = 12 + 1.7*0.9

X = 14

X = 13 (B/O)

Knife https://backpack.tf/item/3940823068

Keys http://backpack.tf/profiles/76561198129519644?time=1442214000&compare=1442473200 https://gyazo.com/aaf8a88bed6a9402f043a7bb203b4c12

Pith https://backpack.tf/item/506610919