How heavy a load (pounds) is needed to pull apart pieces of douglas fir 4 inches long and 1.5 inches square? here are data from students doing a laboratory exercise:

33190 31860 32590 26520 33280

32320 33020 32030 30460 32700

23040 30930 32720 33650 32340

24050 30170 31300 28730 31920

suppose that the strength of pieces of wood like these follows a normal distribution with standard deviation, 3000 pounds. let u (in greek) denote the mean load required to pull the wood apart.

a) give a 95% confidence interval for the mean load required to pull the wood apart.

suppose that the strength of pieces of woodl ike these follows a normal distribution with standard deviation being unknown to us.

b) give a 90% confidence interval for the mean load required to pull the wood apart.