SOLUTION: the lifetimes of a brand of electric light bulbs are normally distributed with mean 1300hours and standartd deviation 120hours. a light bulb is selected at random and tested by ke
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Question 1067247: the lifetimes of a brand of electric light bulbs are normally distributed with mean 1300hours and standartd deviation 120hours. a light bulb is selected at random and tested by keeping it on continuously
find the probability that it has a lifetime of over 1540hours?
its has a lifetime between 1222 and 1540 hours?
two light bulbs are selected at random.
find the probability that they both last between 1222 and 1540
Answer by Boreal(15235) (Show Source): You can put this solution on YOUR website!
z=(x-mean)/sd
=(1540-300/120=2
probability z>2=0.0228
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(1222-1300)/120=-78/120=-0.65
probability -0.65
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That would be the probability just obtained squared, since they are independent: 0.5175 if I don't round the last one.
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