Question

The manager of a grocery store wants to determine what proportion of people who enter his store are his regular customers.  What size sample should he take so that at 99% confidence the margin of error will not be more than 0.1? (Hint: if there is no prior knowledge about the proportion, use 0.5).

Answer 1

Solution :

Given that,

= 0.5

1 - = 1 - 0.5 = 0.5

margin of error = E = 0.1

At 99% confidence level the z is,

= 1 - 99%

= 1 - 0.99 = 0.01

/2 = 0.005

Z_/2 = 2.576

Sample size = n = (Z_/2 / E)² * * (1 - )

= (2.576 / 0.1)² * 0.5 * 0.5

=166

Sample size = 166