I need a formula. I buy inventory and sell it every so many days, 30, 45, etc. I have limited funds so when the inventory sells, I then purchase more. I'm trying to determine how my annual rate of return on my cash will be affected if I 1)change the amount of cash I am using to buy the inventory, 2)change the frequency and amount of inventory purchased (ie once a week purchases of $1000 each versus a monthly purchase of $4000), 3) change how quickly I can convert the inventory back to cash. thanks for the help.