The Villopolis Parks Department has just installed 1900 new lightbulbs with an expected mean lifespan of 66 months and a lifespan standard deviation of 6 months. Assuming normally distributed bulb failure, how many bulbs will need to be replaced after 56 months?
(56-66)/6 = -10/6 = -1.67
95% of them so multiply .95 times 1900