Question 1087049
<font color="black" face="times" size="3">I think you meant to say "sample mean" instead of "population mean". The whole goal of a confidence interval is to estimate the parameter, which in this case is the population mean. If you know the parameter, then why bother estimate it with a confidence interval? 


The sample mean is xbar = 70


The confidence interval is of the form (L, U) where L is the lower endpoint and U is the upper endpoint


If the margin of error is E, then


L = xbar - E
L = 70 - 20
L = 50


and


U = xbar + E
U = 70 + 20
U = 90


Making the confidence interval to be (L, U) = (50, 90) which can be written as {{{50 < mu < 90}}}


Note: {{{mu}}} is the greek letter mu often used in statistics to represent the population mean</font>