Really stuck on this one.
I am trying to work backwards, but the six bulbs is causing my brain problems.
Question is:
Light bulbs lifetime Normally distributed with mean 1100 hours and sd=80 hrs.
Second part of question is where a light fitting of six bulbs in now the subject.
What is the probability that the light fitting can run for t hours without any of the bulbs failing is 0.95. Find t.
Now if the question DIDN'T involve six bulbs I would simply find phi(z) = 0.95, z = 1.645, put that in the z equation to find x and you are done. But the six bulb part is confusing me. How do I incorporate the six bulbs issue into this???