Question

a market surveyor wishes to know how many energy drinks adults drink each week. they want to construct a 80% confidence interval with an error or no more than 0.07. a consultant has informed them that a previous study found the mean to be 7.2 energy drinks per week and found the variance to be 0.81. what is the minimum sample size reauired to create the specified confidence interval?

Answer 1

Solution :

Given that,

variance = 2= 0.81

standard deviation = = 0.9

margin of error = E = 0.07

At 80% confidence level the z is ,

= 1 - 80% = 1 - 0.80 = 0.20

/ 2 = 0.20 / 2 = 0.10

Z/2 = Z 0.10 = 1.280

Sample size = n = ((Z/2 * ) / E)2

= ((1.280 * 0.9) / 0.07)2

= 271

Sample size = 271