If we knew the standard deviation of IQ is 15

If we knew the standard deviation of IQ is 15,(a). How many people do we need to sample if we want the width for 95% confidence to be less than 5?(b). How many people do we need to sample if we want the margin of error for 95% confidence to be less than 3? Hint: Use df = 10 for the t-distribution.

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