Probability related to sample sizes

Reference no: EM13104245

1) A scientist wants a confidence interval of 90% and a margin of error of +-2 for a mean of a Normal population with σ =10. What size samples should she take?

2) A survey of 1600 Democrats and 900 Republicans (all randomly selected) showed at 90% confidence a margin of error of +- 2 for Democrats and +- 3 for Republicans. Why is there a difference?

Reference no: EM13104245

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