Ans Doc 101

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Sixty years ago, a national study of 10 million 14-year-old children found that they could read a complex document at an average speed of 386 words per minute with a standard deviation of 46 words per minute. You are designing a study to learn how fast 12-year-old children can read the same document today. If you want to be 90% confident that the sample mean from your study will be within three words per minute of today’s population mean, how big a sample should you use?