Sample surveys conducted in a large county in a cer-tain year and again 20 years later showed that originally the average height of 400 ten-year-old boys was 53.8inches with a standard deviation of 2.4 inches, whereas20 years later the average height of 500 ten-year-old boyswas 54.5 inches with a standard deviation of 2.5 inches.Use the four steps in the initial part of Section 1 andthe 0.05 level of significance to test the null hypothesisμ1 − μ2 = −0.5 against the alternative hypothesis μ1 −μ2 < −0.5.

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