9. In an experiment, the independent variable is (2 points)
never changed by the scientist
not important to the scientist
not recorded by the scientist
changed by the scientist

Suppose that the life expectancy of a certain brand of nondefective light bulbs is normally distributed, with a mean life of 1100 hr and a standard deviation of 100 hr. if 80 comma 000 of these bulbs are produced, how many can be expected to last at least 1100 hr