I have knowledge about the calculating sample, but i am unable to solve this question for the last two hours. Please check this question.
A bank believes that approximately 2/5 of its checking-account customers have used at least one other service provided by the bank within the last six months.How large a sample will be needed to estimate the true proportion to within 5% at the 98% level of confidence?
The formula for a one proportion Z interval can be switched around to solve for n.
$$n = z^2\frac{p(1-p)}{E^2}$$
$$n = 2.326^2\frac{0.4\cdot 0.6}{.05^2}$$
$$n = 520$$