Question

The number of hours of life of a certain type of torch battery is normally distributed with mean 150 and standard deviation 12. In a quality control test two batteries are chosen at random from a batch.If both batteries have a life less than 120 hours, the batch is rejected.Find the probability that the batch is rejected.

Answer 1

Z = (score-mean)/SD

Find table in the back of your statistics text labeled something like "areas under normal distribution" to find the proportion/probability.

For both, multiply probability by itself.