CFA Practice Question

There are 434 practice questions for this study session.

CFA Practice Question

The lifetime of a 2-volt non-rechargeable battery in constant use has a normal distribution with a mean of 516 hours and a standard deviation of 20 hours. Ninety percent of all batteries have a lifetime less than ______.
A. 517.28 hours
B. 536.00 hours
C. 541.60 hours
Explanation: The z-value corresponding to the proportion 0.9000 is 1.28. We need to use the formula x = u + z σ, where z = 1.28, to get the correct answer, or x = 516 + 1.28 x 20 = 541.6.

User Contributed Comments 5

User Comment
awlhoaln how to get z value is 1.28 ?
johnsk from the z-table.
danlan prob(z<1.645) = 95% and prob(z<1.28)=90%. Note 1.645 used for 5% significance level is for two tail and not one tail!
dimanyc how to get z value for 95%? memorize all your 90%, 95% and 99% values for both both 1 and 2-tailed tests
gaetmichel table will be provided at the exam
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