A new extended-life light bulb has an average service life of 750 hours, with a standard deviation of 50 hours. If the service life of these light bulbs approximates a normal distribution, about what percent of the distribution will be between 600 hours and 900 hours?

Answer 1

Use z-scores.

Formula:

z = (x - mean)/sd

Find two z-scores, using 600 for x and also 900 for x. Mean = 750 and sd = 50.

Once you find the two z-scores, use a z-distribution table to determine your probability between the two z-scores.

Answer 2

-3 3

Answer 3

1. A new extended-life light bulb has an average life of 750 hours, with a standard deviation of 50 hours. If the life of these light bulbs approximates a normal distribution, about what percent of the distribution will be between 600 hours and 900 hours?