Cregg Hart is manufacturing manager for Larabee Engineering, a locomotive engine and rail car manufacturer. The company has been very successful in recent years, and in July 2016 signed two major contracts totaling nearly $200 million. A key to the company’s success has been its focus on quality. Customers from around the world have been very pleased with the attention to detail put forth by Larabee Engineering. One of the things Cregg has been adamant about is that Larabee Engineering’s suppliers also provide high quality. As a result, when the company finds good suppliers, it stays with them and tries to establish a long-term relationship. However, Cregg must also factor in the costs of parts and materials and has instructed his purchasing staff to be on the lookout for “better deals.” Recently, Sheryl Carleson, purchasing manager, identified a new rivet supplier in Europe that claims its rivets are as good or better quality than the current supplier’s but at a much lower cost. One key quality factor is the rivet diameter. When Sheryl approached Cregg about the possibility of going with the new supplier for rivets, he suggested they conduct a test to determine if there is any difference in the average diameter of the rivets from the two companies. Sheryl requested that the new company send 100 rivets, and she pulled a random sample of 100 rivets from her inventory of rivets from the original supplier. She then asked an intern to measure the diameters to three decimal places using a micrometer. The resulting data from both suppliers are given.: Required Tasks: Develop histograms showing the distribution of rivet diameters from the two suppliers. Compute the sample means and standard deviations for the two sets of data. Comment on whether it appears the assumptions required for testing if the two populations have equal mean diameters are satisfied.
Cregg Hart is manufacturing manager for Larabee Engineering, a locomotive engine and rail car manufacturer. The company has been very successful in recent years, and in July 2016 signed two major contracts totaling nearly $200 million. A key to the company’s success has been its focus on quality. Customers from around the world have been very pleased with the attention to detail put forth by Larabee Engineering. One of the things Cregg has been adamant about is that Larabee Engineering’s suppliers also provide high quality. As a result, when the company finds good suppliers, it stays with them and tries to establish a long-term relationship. However, Cregg must also factor in the costs of parts and materials and has instructed his purchasing staff to be on the lookout for “better deals.” Recently, Sheryl Carleson, purchasing manager, identified a new rivet supplier in Europe that claims its rivets are as good or better quality than the current supplier’s but at a much lower cost. One key quality factor is the rivet diameter. When Sheryl approached Cregg about the possibility of going with the new supplier for rivets, he suggested they conduct a test to determine if there is any difference in the average diameter of the rivets from the two companies. Sheryl requested that the new company send 100 rivets, and she pulled a random sample of 100 rivets from her inventory of rivets from the original supplier. She then asked an intern to measure the diameters to three decimal places using a micrometer. The resulting data from both suppliers are given.:
Required Tasks:
- Develop histograms showing the distribution of rivet diameters from the two suppliers.
- Compute the sample means and standard deviations for the two sets of data.
- Comment on whether it appears the assumptions required for testing if the two populations have equal mean diameters are satisfied.
- Select a level of significance for testing whether the two suppliers have rivets with equal mean diameters. Discuss the factors you used in arriving at the level of significance you have selected.
- Perform the appropriate null and alternative hypothesis test. Discuss the results.
- Prepare a short report outlining your recommendation.
Sample Item | Original Supplier | New Supplier |
1 | 0.374 | 0.391 |
2 | 0.387 | 0.375 |
3 | 0.359 | 0.365 |
4 | 0.391 | 0.36 |
5 | 0.39 | 0.366 |
6 | 0.361 | 0.378 |
7 | 0.376 | 0.377 |
8 | 0.371 | 0.364 |
9 | 0.373 | 0.332 |
10 | 0.364 | 0.343 |
11 | 0.39 | 0.378 |
12 | 0.384 | 0.401 |
13 | 0.384 | 0.382 |
14 | 0.383 | 0.381 |
15 | 0.381 | 0.363 |
16 | 0.369 | 0.371 |
17 | 0.361 | 0.352 |
18 | 0.376 | 0.393 |
19 | 0.382 | 0.359 |
20 | 0.368 | 0.367 |
21 | 0.354 | 0.371 |
22 | 0.366 | 0.328 |
23 | 0.359 | 0.37 |
24 | 0.394 | 0.374 |
25 | 0.365 | 0.387 |
26 | 0.39 | 0.374 |
27 | 0.378 | 0.394 |
28 | 0.398 | 0.342 |
29 | 0.366 | 0.373 |
30 | 0.376 | 0.384 |
31 | 0.366 | 0.356 |
32 | 0.392 | 0.366 |
33 | 0.373 | 0.374 |
34 | 0.374 | 0.34 |
35 | 0.375 | 0.347 |
36 | 0.363 | 0.418 |
37 | 0.38 | 0.359 |
38 | 0.398 | 0.36 |
39 | 0.382 | 0.343 |
40 | 0.362 | 0.384 |
41 | 0.362 | 0.389 |
42 | 0.379 | 0.358 |
43 | 0.379 | 0.386 |
44 | 0.369 | 0.365 |
45 | 0.384 | 0.382 |
46 | 0.366 | 0.359 |
47 | 0.376 | 0.389 |
48 | 0.381 | 0.364 |
49 | 0.381 | 0.389 |
50 | 0.373 | 0.387 |
51 | 0.385 | 0.37 |
52 | 0.378 | 0.361 |
53 | 0.392 | 0.391 |
54 | 0.372 | 0.385 |
55 | 0.362 | 0.382 |
56 | 0.371 | 0.374 |
57 | 0.388 | 0.365 |
58 | 0.377 | 0.337 |
59 | 0.384 | 0.414 |
60 | 0.368 | 0.403 |
61 | 0.362 | 0.397 |
62 | 0.372 | 0.39 |
63 | 0.359 | 0.418 |
64 | 0.395 | 0.374 |
65 | 0.37 | 0.369 |
66 | 0.391 | 0.394 |
67 | 0.358 | 0.375 |
68 | 0.376 | 0.38 |
69 | 0.369 | 0.342 |
70 | 0.385 | 0.372 |
71 | 0.398 | 0.386 |
72 | 0.365 | 0.361 |
73 | 0.379 | 0.352 |
74 | 0.397 | 0.406 |
75 | 0.37 | 0.393 |
76 | 0.384 | 0.391 |
77 | 0.368 | 0.391 |
78 | 0.374 | 0.365 |
79 | 0.364 | 0.391 |
80 | 0.376 | 0.353 |
81 | 0.364 | 0.375 |
82 | 0.372 | 0.362 |
83 | 0.381 | 0.388 |
84 | 0.382 | 0.38 |
85 | 0.368 | 0.398 |
86 | 0.375 | 0.384 |
87 | 0.371 | 0.366 |
88 | 0.361 | 0.393 |
89 | 0.374 | 0.385 |
90 | 0.39 | 0.388 |
91 | 0.376 | 0.419 |
92 | 0.374 | 0.358 |
93 | 0.387 | 0.339 |
94 | 0.371 | 0.384 |
95 | 0.36 | 0.357 |
96 | 0.386 | 0.363 |
97 | 0.377 | 0.437 |
98 | 0.365 | 0.38 |
99 | 0.374 | 0.378 |
100 | 0.363 | 0.369 |
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