A company installs 5000 light bulbs, each with an average life of 500 hours and a standard deviation of 100 hours, and a distribution approximated by a normal curve. Find the percentage of bulbs that can be expected to last the period of time between 540 hours and 780 hours? Less than 690 hours?© BrainMass Inc. brainmass.com December 24, 2021, 4:44 pm ad1c9bdddf
1) Here we take Sd=100 as the population Sd, which is already known.
We are to solve Pr(540<X<780)=Pr(X<780)- ...
The standard distribution curve is used to calculate probabilities.