A Casino has 4 roulette tables. Each table needs to be measured for bias and when one fails the test the wheel must be taken to a shop and cleaned and balanced. Currently each wheel needs to be serviced in this fashion at a rate of about once every 10 days. The servicing process takes an average of about 2 days. The shop employs one tech to fix the machines. On average how many roulette tables are operable (capable of being used) at any given time in the casino (most nearly)