Solution: The mean $A_n = \frac{X_1 + ... + X_{80}}{80}$ is approximately normally distributed. Using $n = 80$, $\hat{p} = 5/8$, and $s^2 = 15/64$, we have a 95% confidence interval:
$p_l = \hat{p} - 1.96\left(\frac{s}{\sqrt{n}}\right) \approx 0.52$
$p_h = \hat{p} + 1.96\left(\frac{s}{\sqrt{n}}\right) \approx 0.73$