SOLUTION: A researcher wishes to estimate, with 95% confidence, the proportion of adults who have high-speed internet access. Her estimate must be accurate within 4% of the true proportion. 

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Question 1075549: A researcher wishes to estimate, with 95% confidence, the proportion of adults who have high-speed internet access. Her estimate must be accurate within 4% of the true proportion. 
a) find the minimum sample size needed, using a prior study that found 52% of the respondents said they have high-speed internet access. 
b) No preliminary estimate is available. Find the minimum sample size needed. 
Show your work, if is you used technology - explain your steps.
Answer by Boreal(15235) About Me  (Show Source):
You can put this solution on YOUR website!
the interval is +/- z*sqrt{p*(1-p)/n}
That is 1.96*sqrt(0.52*0.48)/n=0.04, the size of the interval.
square everything and then multiply both sides by n
3.8416(.2496)=0.0016n
divide both sides by 0.0016
599.29 rounded to 600.
Calculator for the calculations.
Can check with calculator for 1 sample proportion using 312 and 600 (52%) then asking for 95% CI. The interval is 4% on either side. of 52%.