Two-sample proportion procedures worksheet
1) Covariant Industries outsources its paperwork imaging needs to two companies: Endomorphism Inc.
and Tensor Limited. The paperwork coordinator is curious which company is better at getting documents
onto the imaging system within 24 hours. She selects an SRS of documents sent to each company and
determines how many of these documents were placed in the imaging system within 24 hours. Here are the
results of the study:
Company Documents proccessed within 24 hours Documents in sample
Endomorphism Inc. 249 515
Tensor Limited 125 218
a) Find a 95% confidence interval for the difference between the proportion of documents processed
within 24 hours by Endomorphism Inc. and the proportion for Tensor Limited.
b) Is there significant evidence, at the 5% level, that the proportions of documents processed within 24
hours by Endomorphism Inc. is different than the proportion for Tensor Limited? (Hint: you can carry out
this significance test by using the interval above.)
2) A political polling firm is interested in differences in voting behavior between men and women. They
conduct an SRS of registered voters, ask them how they plan to vote in an upcoming election between R.
Green and J. Bleau, and get the following results:
Sex R. Green J. Bleau Undecided
Male 305 328 41
Female 410 329 31
a) Find a 99% confidence interval for the difference between the proportion of all male voters voting for
Green and the proportion of all female voters voting for Green.
b) Find a 99% confidence interval as above, but this time only consider voters who have made a decision.
(In other words, throw out undecided voters.)
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