The hours of sleep each day for American adults are assumed to be normal with a mean of 6.8 hours and standard deviation of 0.9 hours. Answer the following round answers to 3 decimal places. 1. How many hours per day must you sleep tonight to be in the 25th percentile? 2.find the probability that a randomly selected American sleeps somewhere between 6.1 and 7.5 hours per day 3. Find the probability that a random sample of 9 Americans will have a mean of more than 7.2 hours of sleep per day