Green sawmill buys sustainably produced hardwood logs and uses ultra-efficient sawing technique to produce lumber for the furniture and ship-building industries. For its teak wood lumber green sawmill buys 12.5-foot-long logs from known sustainable sources. Green sawmill wants to know how much usable lumber it gets from a log. A random sample of 100 logs are carefully sawn and quantity of usable lumber tabulated for each log in the samples. The sample yielded a mean of 60 board- feet. You may assume that the population distribution of the quantity of lumber ( in board- feet) obtained from a log is normal with a now standard deviation of 20 board- feet.

• Write down a 95% confidence interval for the population mean number of board feet of lumber obtained from log (enter the upper bound of the confidence interval)
• Teak lumber sells $50 per board foot. What us your estimate for the mean dollar value of lumber obtained from a log
• Write down a 95% confidence interval for the mean dollar value of lumber obtained from a log ( enter the upper bound of the confidence interval)
• What sample size would be needed to make the 95% confidence interval in part A five board-feet wide?