As a manager for an advertising company, you must plan a campaign designed to increase Twitter usage. A recent survey suggests that 85% of adults know what Twitter is. How many adults should you survey in order to be 90% confident that your estimate is within 5% of the true population proportion?

Answer 1

Solution
Our p in this case is 0.85
Our q will be 1-p, which is 1-0.85
The Margin of Error will be 0.05,
Z*-value will be 1.645, as read from the table
Therefore, n will be given by

n= pq(z/ME)2

n= 0.85*(1-0.85) *{1.645/0.05)2
n=138.0007, approx. 138 adults