Answer: 5
Step-by-step explanation:
The formula for calculating margin of error for the population mean is expressed as
margin of error = z x σ/√n
where
z is the z score for a 90% confidence level. From the normal distribution table, z = 1.645
σ is the population standard deviation
n is the sample size or number of website that should be checked.
From the information given,
σ = 56
margin of error = 40
By substituting these values into the formula, we have
40 = 1.645 x 56/√n
40 = 92.12/√n
By cross multiplying, we have
40√n = 92.12
√n = 92.12/40
Squaring both sides,
n = (92.12/40)^2
n = 5.3
Approximately, number of website that should be checked is 5