Question

3. A legislative aide doing research on the duration of calls initiated on cell phones. A preliminary study showed that the standard deviation is 1.7. "How large" a sample is needed for the aide to be able to state with 99% confidence the sample mean differs from the population mean by no more than 0.20 minutes.

Answer 1

Solution :

Given that,

standard deviation = =1.7

Margin of error = E = 0.20

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

n = ( 2.576* 1.7/ 0.20)²

n =479.43

Sample size = n =479