SOLUTION: A new type of light bulb has an average lifespan of 1200 hours with a standard deviation of 75 hours. Use the table to find the probability that a light bulb chosen at random will

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Question 870617: A new type of light bulb has an average lifespan of 1200 hours with a standard deviation of 75 hours. Use the table to find the probability that a light bulb chosen at random will last more than 1155 hours.Please help me :)
Answer by jim_thompson5910(35256) About Me  (Show Source):
You can put this solution on YOUR website!
Find the z-score

z = (x-mu)/sigma
z = (1155-1200)/75
z = -0.60


Use this table to find that the area to the left of z = -0.60 is 0.2743

So the area to the right of z = -0.60 is 1 - 0.2743 = 0.7257


Answer: the probability that a light bulb chosen at random will last more than 1155 hours is approximately 0.7257 (about a 72.57% chance)