Question 1010455
The life expectancy of a typical lightbulb is normally distributed with a mean of 1,975 hours and a standard deviation of 25 hours. What is the probability that a lightbulb will last between 1,950 and 2,050 hours? 
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z(1950) = (1950-1975)/25 = -1
z(2050) = (2050-1975)/25 = 75/25 = 3
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P(1950< x <2050) = P(-1< z <3) = 0.84
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Cheers,
Stan H.
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0.84 
0.77 
0.82 
0.89