- CFA Exams
- CFA Level I Exam
- Study Session 3. Quantitative Methods (2)
- Reading 9. Common Probability Distributions
- Subject 6. The Normal Distribution

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**CFA Practice Question**

The time it takes an auto mechanic to replace a carburetor is known to follow a normal distribution with a mean of 53 minutes and a standard deviation of 7.5 minutes. This means that ______

A. about 68% of the time it takes between 45.5 minutes and 53 minutes to replace a carburetor.

B. about 68% of the time it takes between 53 minutes and 60.5 minutes to replace a carburetor.

C. about 95% of the time it takes between 38 minutes and 68 minutes to replace a carburetor.

**Explanation:**95% of the observations lie within μ +- 2 σ or (38,68).

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**User Contributed Comments**
4

User |
Comment |
---|---|

mchu |
according to the notes, the empirical rule applies only to distributions when 95% of the data points fall within two standard deviations of the mean. |

StanleyMo |
68% of the observations fall within 1 standard . 95% of the observations fall within 2 standard . 99.7% of the observations fall within 3 standard |

sagrr |
68 1 95 2 99.7 3 ! |

NikolaZ |
68% of the values fall within 1 standard deviation of the mean. And 95% of values fall within 1.96 standard deviations of the mean, not 2. |