Nacirema Airlines Is Buying a Fleet of New Fuel-Efficient Planes $\quad$

question 59

Multiple Choice

Nacirema Airlines is buying a fleet of new fuel-efficient planes. The HogJet and the LitheJet both meet their price and performance needs, and both planes meet EPA noise guidelines. However, the quieter plane is preferred. Each plane is flown through a typical takeoff and landing sequence 10 times, while remote sensors at ground level record the noise levels (in decibels) . The table below summarizes the sound level tests using Excel's default level of significance (? = 0.05) . $\quad$$\quad$$\text { t-Test: Assuming Equal Variances }$ $\quad$$\quad$$\quad$$\quad$ $\text { t-Test: Assuming Unequal Variances }$

$\begin{array}{l}\begin{array} { lrr } &\text { takeJet } &\text { HogJet } \\\text { Mean } & 80.3368 & 82.4669 \\\text { Variance } & 0.7178 & 4.7385 \\\text { Observations } & 10 & 10 \\\text { Pooled Variance } & 2.7282 & \\\text { Hypothesized Diff } & 0.0000 & \\\text { df } & 18 \\\text { t Stat } & -2.8837 \\\text { P(T eat) one-tail } & 0.0049 \\\text { t Critical one-tail } & 1.7341 \\\text { P(T =-t) two-tail } & 0.0099 \\\text { t Critical two-tail } & 2.1009 &\end{array}\begin{array} { lrr} &\text { takeJet } &\text { HogJet } \\\text { Mean } & 80.3368 & 82.4669 \\\text { Variance } & 0.7178 & 4.7386 \\\text { Observations } & 10 & 10 \\\text { Hypothesized Diff } & 0 & \\\\\text { df } & 12 \\t \text { Stat } & -2.8837 \\\text { P(T } \text { ett ) one-tail } & 0.0069 \\t \text { Critical one-tail } & 1.7823 \\\mathrm{P}(\mathrm{T}<=\mathrm{t}) \text { two-tail } & 0.0137 \\\mathrm{t} \text { Critical two-tail } & 2.1788\end{array}\end{array}$
After inspecting this table, we would most likely:

• A)use the test assuming unequal variances.
• B)use the test for equal variances.
• C)perform another test to determine if the variances are equal before proceeding.
• D)realize that the decision isn't affected by our assumptions concerning the variance.

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