i) a) A paediatrician wants to estimate the mean weight of firstborn babies which is normally distributed. The standard deviation of weight for all firstborn babies is 1.15 kg. If she wants to be 94%...

i) a) A paediatrician wants to estimate the mean weight of firstborn babies which is

normally distributed. The standard deviation of weight for all firstborn babies is 1.15

kg. If she wants to be 94% sure that the mean weight of firstborns differs from their

sample mean by no more than 0.25 kgs, what should be the size of the sample?
b) For a given sample size, why is a 90% confidence interval smaller than 99%.

Wouldn’t it always be desirable to reduce the interval width in this manner?