Starbucks has found that 23% of customers purchase more than one cup of coffee per day from their shops. Suppose you randomly choose 215 of today's Starbucks customers.
1) Find the probability that no less than 31% of them purchased more than one cup of coffee from Starbucks.
On the SAT, the average Writing score is 475 points and the average Mathematics score is 521 points. The standard deviation is 80 points on each part of the test. Now suppose 60 test takers are selected.
2) 10% of the time the sample average Mathematics score should be less than what?
The number of hours adults sleep per night is normally distributed with a mean of 6.6 hours. Assume the standard deviation is unknown.
3) If 65% of adults sleep more than 5.8 hours per night , what is the variance?
**Please round answers to 4 decimal places**