The mean life of a particular brand of light bulb is 1000 hours and the standard deviation is 50 hours. Tests show that the life of the bulb is approximately normally distributed. It can be concluded that approximately 68% of the bulbs will last between a. 900 and 1100 hours b. 950 and 1050 hours c. 850 and 1150 hours d. 800 and 1200 hours