The mean time that a certain model of light bulb will last is 300 hours, with a standard deviation equal to 150 hours. a. Calculate the standardized value for a light bulb that lasts 600 hours. b. Assuming that the distribution of hours that light bulbs last is bell-shaped, what percentage of bulbs could be expected to last longer than 600 hours? a. The standardized value for a light bulb that lasts 600 hours is (Type an integer or decimal rounded to two decimal places as needed.) b. Assuming that the distribution of hours that light bulbs last is bell-shaped, the percentage of bulbs that could be expected to last longer than 600 hours is % (Type an integer or decimal rounded to one decimal place as needed.)