Answer: d. 122
Step-by-step explanation:
Formula to find sample size : [tex]n=\left ( \dfrac{\sigma\times z}{E} \right )^2[/tex] , where [tex]\isigma[/tex] = prior population standard deviation, z= Critical z-value for confidence level and E = Margin of error.
As per given ,
[tex]\sigma=90\ hours\\\\E=\pm16\ hours[/tex]
Also , for 95% confidence level , z-value = 1.96
Now , Required sample size would be
[tex]n=\left ( \dfrac{90\times1.96}{16} \right )^2\\\\=\left(11.025\right)^2\\\\=121.550625\approx122[/tex]
Hence, the required sample size =122
Thus , the correct option is d. 122.
