Brianna went to the store to buy some clothes. She bought 9 pairs of pants at $20 per pair of pants, and 11 shirts that cost $15
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And we got so then the value for
and then the confidence level is given by:
represent the real population proportion for 1
represent the estimated proportion for 1
is the sample size required for 1
represent the real population proportion for 2
represent the estimated proportion for 2
is the sample size required for 2
represent the critical value for the margin of error
The population proportion have the following distribution
The confidence interval for the difference of two proportions would be given by this formula
For this case we have the confidence interval given by: (-0.0313,0.2753). From this we can find the margin of erro on this way:
And we know that the margin of erro is given by:
We have all the values except the value for
So we can find it like this:
And solving for we got:
And we can find the value for with the following excel code:
"=1-NORM.DIST(2.326,0,1,TRUE)"
And we got so then the value for
and then the confidence level is given by:
or 98%