The mean of 10 observations is 12.5 . While calculating the mean one observation was by mistake taken as -8 instead of +8 . Find the correct mean.

A group of students with normally distributed salaries earn an average of $6,800 with a standard deviation of $2,500. What proportion of students earn between $6,500 and $7,300?

What is the term used in talking about the chance that an event occurs?

What is the area under the standard normal curve?