Question

Mike wishes to estimate the mean number birds that visit his bird feeder each day. The population standard deviation (σ) is known from past studies to equal 12 birds. If Mike wishes to be 90% confident of getting an estimate within 3 birds of the true mean, what sample size is required?

Answer 1

Solution :

Given that,

standard deviation =   =12

Margin of error = E = 3

At 90% confidence level

= 1 - 90%  

= 1 - 0.90 =0.10

/2 = 0.05

Z/2 = Z0.05 = 1.645

sample size = n = [Z/2* / E] 2

n = ( 1.645 *12 /3 )2

n =43.296

Sample size = n =44