TDSM 5.3

(a) $$B(100, 0.5) \approx N(100 \times 0.5, 100 \times 0.5 \times 0.5) = N(50, 25)$$

$$P(X \geq 70) = 1 - P(X \lt 70) = 1 - P \left( Z \lt \frac{70-50}{\sqrt{25}} \right) = 1 - P(Z\lt 4) \approx 0$$