Question

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: 33,190 31,860 32,590 26,520 33,280 32,320 33,020 32,030 30,460 32,700 23,040 30,930 32,720 33,650 32,340 24,050 30,170 31,300 28,730 31,920 Suppose that the strength of pieces of wood like these follows a Normal distribution with standard deviation 3000 pounds. Give a 95% confidence interval for the mean load required to pull the wood apart.

Answer 1

Answer:

Step-by-step explanation:

Given that data from students doing a lab exercise are as follows:

33,190 31,860 32,590 26,520 33,280 32,320 33,020 32,030 30,460 32,700 23,040 30,930 32,720 33,650 32,340 24,050 30,170 31,300 28,730 31,920

Mean = 30841

Since normal and also sigma is known, std error

=$\frac{\sigma}{\sqrt{n} } \\=\frac{3000}{\sqrt{40} } \\=474.34$

For95% margin of error = ±1.96(474.34) =±929.71

Hence 95% conf interval = 30841±929.71

=(29911.29, 31770.71)