The article "Urban Battery Litter" cited in Example 8.14 gave the following summary data on zinc mass (g) for two different brands of size D batteries:

Assuming that both zinc mass distributions are at least approximately normal, carry out a test at significance level .05 to decide whether true average zinc mass is different for the two types of batteries.

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Brand Sample Size Sample Mean Sample SD Duracell Energizer 7.76 1.52 15 20 138.52 149.07