Question

I am not able to tackle this question. Somebody please help me out

Answer 1

The wire breaks if the load $X$ exceeds some amount. So what you're asked to do is find $P(X\ge74)$ and $P(X\ge89)$.

In either case, transform $X$ to the random variable $Z$ that's normally distributed with expected value 0 and standard deviation 1.

$P(X\ge74) = P\left(\dfrac{X-80}3 \ge \dfrac{74-80}3\right) \\ = P(Z \ge -2) \\ = 1-P(Z < -2) \approx 0.9773$

$P(X\ge89) = P\left(\dfrac{X-80}3 \ge \dfrac{89-80}3\right) \\= P(Z \ge 3) \\= 1 - P(Z < 3) \approx 0.0013$

Answer 2

B would be the answer for this question