A person recently read that 82% of cat owners are women. How large a sample should the person take it she wishes to be 90% confident that her proportion is within 0.03 of the true population proportion?
Solution :
Given that,
= 0.82
1 -
= 1 - 0.82 = 0.18
margin of error = E = 3% = 0.03
At 90% confidence level
= 1 - 0.90 = 0.10
/2
=0.05
Z/2
= 1.645 ( Using z table )
Sample size = n = (Z/2
/ E)2 *
* (1 -
)
= (1.645 / 0.03)2 * 0.82 * 0.18
=443.78
Sample size = 444
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