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Applications with Standard Normal Distribution

Question 34 • AZ-Common Core Algebra II B

The life of a certain brand of battery is normally distributed, with mean 128 hours and standard deviation 16 hours. What is the probability that a battery you buy lasts at most 100 hours? Standardize the variable.x = 100 is equivalent to z = .

Answer
A
–0.57
B
0.57
C
–1.75
D
1.75

Explanation

Standardize using z = (x − mean) / standard deviation. For x = 100, z = (100 − 128) / 16 = −28 / 16 = −1.75, so 100 hours corresponds to z = −1.75 (choice C).

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