17.4 In a stratified random sample of individuals—male and female—in Porvoo, Finland, sample members were asked to share the amount of time they spent on reading (in hours) per week. The results had been recorded and are shown in the accompanying table.

Male (M) Female (M)

Ni 450 550 ni 25 25 xi 8.75 14.6 si 1.25 0.94

a. Find a 90% confidence interval for the mean reading time provided by all the male members.

b. Find a 95% confidence interval for the mean reading time provided by all the female members.

c. Find a 99% confidence interval for the mean reading time that is given by all the individuals in Porvoo, Finland.