434 CHAPTER 8 Hypothesis Testing with Two Samples 20. Tensile Strength An engineer wants to compare the tensile strengths of steel bars that are produced using a conventional method and an experimental method. (The tensile strength of a metal is a measure of its ability to resist tearing when pulled lengthwise.) To do so, the engineer randomly selects steel bars that are manufactured using each method and records the tensile strengths (in newtons per square millimeter) listed below. Experimental Method: 395 389 421 394 407 411 389 402 422 416 402 408 400 386 411 405 389 410 Conventional Method: 362 352 380 382 413 384 400 378 419 379 384 388 372 383 At a = 0.10, can the engineer support the claim that the experimental method produces steel with a greater mean tensile strength? Assume the population variances are not equal. 21. Teaching Methods A new method of teaching reading is being tested on third grade students. A group of third grade students is taught using the new curriculum. A control group of third grade students is taught using the old curriculum. The reading test scores for the two groups are shown in the back-to-back stem-and-leaf plot. Old Curriculum New Curriculum 9 3 9 9 4 3 98843321 5 24 76422100 6 011477777899 7 01123349 8 2 4 Key: 90 40 3 = 49 for old curriculum and 43 for new curriculum At a = 0.10, is there enough evidence to support the claim that the new method of teaching reading produces higher reading test scores than the old method does? Assume the population variances are equal. 22. Teaching Methods Two teaching methods and their effects on science test scores are being reviewed. A group of students is taught in traditional lab sessions. A second group of students is taught using interactive simulation software. The science test scores for the two groups are shown in the back-to-back stem-and-leaf plot. Traditional Lab Interactive Simulation Software 4 6 99887663210 7 0455778 98511100 8 003478899 2 0 9 1 3 9 Key: 00 90 1 = 90 for traditional and 91 for interactive At a = 0.01, can you support the claim that the mean science test score is lower for students taught using the traditional lab method than it is for students taught using the interactive simulation software? Assume the population variances are equal.
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