college STATISTICS
posted by HELP .
Sample of 80 people randomly asked in casino shows that average lost per person is $160 with a standard deviation รณ = $40. Based on this data create a 99% confidence interval for population mean. Does loss of $180 for single person contradict expectation? Explain your answer.

Formula:
CI99 = mean + or  2.575 (sd/√n)
Substitute what is given into the formula:
CI99 = 160 + or  2.575 (40/√80)
I'll let you take it from here. Once you have the interval calculated, you should be able to answer the question in the problem.
I hope this will help get you started. 
What does "or" mean?