33220 32290 23090 24010 31830 33010 30970 30120 32630 32030

33,220 32,290 23,090 24,010

31,830 33,010 30,970 30,120

32,630 32,030 32,660 31,320

26,510 30,470 33,600 28,770

33,260 32,730 32,340 31,950

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. (a) We are willing to regard the wood pieces prepared for the lab session as an SRS of all similar pieces of Douglas fir. Engineers commonly assume that characteristics of materials vary Normally. Make a graph to show the shape of the distribution for these data. (Do this on paper. Your instructor may ask you to turn in this work.) Does the Normality condition appear safe? Suppose that the strength of pieces of wood like these follows a Normal distribution with standard deviation 2750 pounds. (Select all that apply.)

Solution

Prepare histogram and find that this is not normal shape.

The data do not appear to follow a Normal distribution.

b) 90% confidence level we calculate mean and std dev

Total Numbers

20

Mean (Average)

30840.5

Population Standard deviation

2937.384

Confidence interval lower bound = 30840.5-1.68(2937.384)

Upperbound = 30840.5+1.68(2937.384)

Confidence interval = (25905.69, 35775.31)

	Frequency
23090 - 24142	2
24142 - 25194	0
25194 - 26246	0
26246 - 27298	1
27298 - 28350	0
28350 - 29402	1
29402 - 30454	1
30454 - 31506	3
31506 - 32558	5
32558 - 33610	7