The formula for the margin of error is given by :
Where SD = standard deviation
n = sample size
z = z-value at 95% confidence level which is always equal to 1.96
and MOE = Margin of Error
Solving for the margin of error :
The margin of error is
Solving for the confidence interval :
CI = 83 - 2.18 = 80.82
CI = 83 + 2.18 = 85.18
So the confidence interval is 80.82 to 85.18