The Mean Life of a Particular Brand of Light Bulb

Multiple Choice

The mean life of a particular brand of light bulb is 1200 hours and the standard deviation is 50 hours.It can be concluded that at least 89% of this brand of bulbs will last between _______.

A) 1100 and 1300 hours
B) 1150 and 1250 hours
C) 1050 and 1350 hours
D) 1000 and 1400 hours
E) 950 and 1450 hours