Not sure, if this doesn't bode well you're free to steal my proof

Sale 1 OUTLIER

http://www.tf2outpost.com/trade/25145654 Sold for Spec KS Aussie Grenade + 1 key

Grenade has about ~ 4.3 keys in parts

B/O for Crown was 55 keys (5 buds)

B/O for Grenade was 32 keys

X = (26.4 + 4.3)*0.9 + 1

X = 29

Grenade https://backpack.tf/item/2404948161

Crown https://backpack.tf/item/3540253870

Mini for Nade

http://steamcommunity.com/market/listings/440/Strange%20Specialized%20Killstreak%20Australium%20Grenade%20Launcher Sold for $68.11 on Feb 26th

$68.11 + $68.11/1.15 = $127.34

$127.34/2 = $63.67

Keys were $2.41 at time of sale

63.67/2.41 = 26.4 keys

Sale 2

http://www.tf2outpost.com/trade/25251909 Sold for Glory Guad

X = 47*0.9

X = 42 keys

Guad https://backpack.tf/item/3566169438

Crown https://backpack.tf/item/3540253870

Notable Trade

http://www.tf2outpost.com/trade/25218920 Denied DaD Tricorne (29 keys), possibly proving Sale 1 is a quicksell.

Also the Guad was offered on the Tavish.