Answer: 705
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Explanation:
mu = population mean = 1300
sigma = population standard deviation = 20
Compute the z score based on x = 1330
z = (x-mu)/sigma
z = (1330-1300)/20
z = 30/20
z = 1.5
Asking to compute P(X < 1330) is the same as P(Z < 1.5) in this specific context when mu = 1300 and sigma = 20.
Use a Z table or a calculator to find that P(Z < 1.5) is roughly 0.93319
About 93.319% of the 755 bulbs are expected to last less than 1330 hours.
0.93319*755 = 704.55845
That value rounds to 705
