Answer
n $\approx$ 7
Work Step by Step
1) The z-score corresponding to an 80% Confidence level is 1.28
2) Substitute z = 1.28, $\sigma$ = 4.1 and E = 2 into the formula:
n = $(\frac{z \times \sigma}{E})^{2}$
n = $(\frac{1.28 \times 4.1 }{2})^{2}$
n $\approx$ 6.885
n $\approx$ 7
