SPA 3e_ Teachers Edition _ Ch 6
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STATS applied!<br />
How can we build “greener” batteries?<br />
Kids love getting toys for their birthdays, especially electronic ones that have flashing lights<br />
and make loud noises. But these devices require lots of power and can drain batteries quickly.<br />
Battery manufacturers are constantly searching for ways to build longer-lasting batteries.<br />
When the manufacturing process is working correctly, AA batteries from a particular<br />
company should last an average of 17 hours, with a standard deviation of 0.8 hours. Also,<br />
at least 73% of the batteries should last 16.5 hours or more.<br />
Quality-control inspectors select a random sample of 50 batteries during each hour of<br />
production and then drain them under conditions that mimic normal use. The graph and<br />
summary statistics describe the distribution of the lifetimes (in hours) of the batteries from<br />
one sample of 50 AA batteries.<br />
Frequency<br />
12<br />
10<br />
8<br />
6<br />
4<br />
2<br />
15.0 15.5 16.0<br />
16.5 17.0 17.5 18.0 18.5<br />
Lifetime (h)<br />
n Mean SD min Q 1 med Q 3 max<br />
50 16.718 0.66 15.46 16.31 16.7 17.28 17.98<br />
Do these data suggest that the production process isn’t working properly? Or is it safe<br />
for plant managers to send out all the batteries produced in this hour for sale?<br />
Teaching Tip:<br />
STATS applied!<br />
The STATS applied! feature is designed<br />
to appeal to students and preview<br />
interesting questions that statistics<br />
can answer. To answer this STATS<br />
applied!, students must make inferences<br />
about a population from sample data.<br />
Knowledge of the sampling distribution<br />
of the sample proportion p^ and the<br />
sampling distribution of the sample<br />
mean x are needed to answer this<br />
question, although students won’t<br />
understand why until the end of the<br />
chapter. However, students should<br />
understand that this question is<br />
about quality control, an important<br />
statistical application for manufacturing<br />
businesses.<br />
We’ll revisit STATS applied! at the end of the chapter, so you can use what you have learned to help<br />
answer these questions.<br />
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C H A P T E R 6 • Sampling Distributions<br />
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