https://marketplace.tf/items/tf2/31200;5;u35

https://backpack.tf/item/10424139989

May 31: $41.99/1.99=21.1 ~21 keys

July 21: $41.99/1.956=21.46 ~21 keys

July 25 : $41.99/1.95=21.53 ~22 keys

August 6 : $41.99/1.997=21.02 ~21 keys

August 19 : $41.99/2.012=20.86 ~21 keys

key prices https://marketplace.tf/items/tf2/5021;6

May 29 1.99

July 21 (1.97+1.97+1.95+1.95+1.95+1.95+1.95)/7=1.956

July 25 1.95

August 6 (1.95+1.95+2+2.01+2.05+2.04+1.98)/7=1.997

August 19 (2.05+2.02+2.02+2.02+2+2+2)/7=2.012

taking 21-22 keys here