Fuel Efficiency of Automobiles Twelve automobiles were tested to see how many miles per gallon each one obtained. Under similar driving conditions, they were tested again, using a special additive. The data are shown here. At a = 0.05, did the additive improve gas mileage? Use the Wilcoxon signed-rank test.
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Before
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After
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13.6
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18.3
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22.6
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23.7
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18.2
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19.5
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21.9
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20.8
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16.1
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18.2
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25.3
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25.3
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15.3
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16.7
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28.6
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27.2
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19.2
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21.3
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15.2
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17.2
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18.8
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17.2
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16.3
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18.5
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