The minimum injection pressure (psi) for injection molding specimens of high amy
ID: 1189857 • Letter: T
Question
The minimum injection pressure (psi) for injection molding specimens of high amylose corn was deter-mined for eight different specimens (higher pres-sure corresponds to greater processing dif culty), resulting in the following observations (from Ther-moplastic Starch Blends with a Polyethylene-Co-Vinyl Alcohol: Processability and Physical Proper-ties, Polymer Engrg. & Sci., 1994: 17—23):
15.0 13.0 18.0 14.5 12.0 11.0 8.9 8.0
Suppose we want the values of the sample mean and median when the observations are expressed in kilograms per square inch (ksi) rather than psi. Is it necessary to reexpress each observation in ksi, or can the values calculated in part (a) be used directly? Hint: 1 kg 2.2 lb.
Explanation / Answer
We can use the values directly and later convert the answers in ksi.
S.No
Sample
1
8
2
8.9
3
11
4
12
5
13
6
14.5
7
15
8
18
Total
100.4
Mean = sum of samples/no. of samples
= 100.40/8
= 12.55
Mean in ksi = 12.55/2.2 =5.70
Median = (n+1)/2 th item
= (8+1)/2 th item
= 4th item/ 2 + 5th item /2
= 12/2 +13/2
= 12.50
median in ksi = 12.50/2.2 =5.68
S.No
Sample
1
8
2
8.9
3
11
4
12
5
13
6
14.5
7
15
8
18
Total
100.4
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