4. The article Urban Battery Litter gave the following summary data on zinc mass

Question

4. The article Urban Battery Litter gave the following summary data on zinc mass (g) for two different brands of size D batteries: Brand Sample Size Sample Mean Sample SD Duracell 15 20 138.52 149.07 7.76 1.52 Energizer Assuming that both zinc mass distributions are at least approximately normal. (a) Estimate the ratio of the variances for two brands using a 95% confidence interval. Can you assume the equal variance? (b) Estimate the difference of true average zinc mass for the two types of batteries using a 95% confidence interval. Is there any evidence showing that the true average zinc mass is different for the two types of batteries?

Explanation / Answer

Two-sample t-test on summary data Results Summary results Sample 1 Sample 2 Mean 138.52 149.07 Standard deviation 7.76 1.52 n 15 20 Standard error 2 0.34 95% CI for mean (-14.07     -6.95) DF 14 19 33 t -5.96 P-value 0 Tails 1-tailed Conclusion Accect null hypothesis:
means differ

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