Dear all,
Would hope somebody could explain to me part b. Thank you so much!
What I did is: margin of error<=0.06 ->
but then the answer is below. Since p depends on n, how can the answer keep the same proportion (0.6x0.4+0.375*0.625). 
"In a market research study to compare two chocolate bar wrappings,
30 out of 50 children preferred a gold wrapping to a silver wrapping, whereas 25 out of 40 adults preferred the silver wrapping.
(a) Compute a 95% confidence interval for the difference in the true proportions in
favour of gold wrapping between the two groups.
(b) It is decided to take further samples of children and adults so that we nally
sample the same number of adults and children such that the nal estimator of
the difference between proportions is within 0.06 of the true difference (with
95% confidence). How many more adults and children need to be sampled?"
Would hope somebody could explain to me part b. Thank you so much!
What I did is: margin of error<=0.06 ->
but then the answer is below. Since p depends on n, how can the answer keep the same proportion (0.6x0.4+0.375*0.625). "In a market research study to compare two chocolate bar wrappings,
30 out of 50 children preferred a gold wrapping to a silver wrapping, whereas 25 out of 40 adults preferred the silver wrapping.
(a) Compute a 95% confidence interval for the difference in the true proportions in
favour of gold wrapping between the two groups.
(b) It is decided to take further samples of children and adults so that we nally
sample the same number of adults and children such that the nal estimator of
the difference between proportions is within 0.06 of the true difference (with
95% confidence). How many more adults and children need to be sampled?"