First: Your calculation of the total lbs of 8 Live cattle = 320,000 less the total lbs. of 4 Feeders = 200,000 to get the total weight gain of 120,000 lbs is correct.
My calculation as stated is based on 500 lbs gain per Head. 1 feeder = 50,000 / 750 = 66.66666666666+ head. 2 Live @ 40,000...