Question

If the variance of the water temperature in a lake is 25°, how many days should the researcher select to measure the temperature to estimate the true mean within 2° with 90% confidence?  

Answer 1

Solution :

Given that,

Population standard deviation () = = 25 = 5

Margin of error = E = 2

Z/2 = 1.645

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

n = [1.645 * 5/ 2]2

n = 17

Sample size = 17

Researcher should select 17 days to measure the temperature.