A large population has a mean of 518 and a standard deviation of 9.9. A sample of 220 from the population has a standard deviation of 10.6. An interval estimate for ?μ based on that sample was...

A large population has a mean of 518 and a standard deviation of 9.9. A sample of 220 from the population has a standard deviation of 10.6. An interval estimate for ?μ based on that sample was determined to be (519.55, 520.85).

What was ?⎯⎯⎯x¯ for the sample?