Question

For a particular brand of SUV, you want to estimate the miles per gallon (mpg). The manufacturer says that σ = 1.75 mpg. Find the sample size if you want a margin of error of ± 0.55 and 90% confidence?

Answer 1

Solution :

Given that,

standard deviation = = 1.75

margin of error = E = 0.55

At 90%confidence level the z is ,

   = 1 - 90% = 1 - 0.90 = 0.10

/ 2 = 0.10 / 2 = 0.05

Z/2 = Z0.05 = 1.645

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

= ((1.645 * 1.75) /0.55 )2

= 27

Sample size = 27