Frequently data must be treated as a sample, although at first
sight they appear to be a complete enumeration. A proprietor of a
parking lot finds that business is poor on Sunday mornings. After
26 Sundays in operation, his average receipts per Sunday morning
are exactly $10. The standard error of this figure, computed from
week-to-week variations, is $1.2. The attendant costs $7 each
Sunday. The proprietor is willing to keep the lot open at this time
if his expected future profit is $5 per Sunday morning. What is the
confidence probability that the long-term profit rate will be at
least $5? What assumption must be made in order to answer this
question?