- CFA Exams
- CFA Level I Exam
- Study Session 2. Quantitative Methods (1)
- Reading 8. Probability Concepts
- Subject 3. Addition Rule for Probabilities: the Probability that at Least One of Two Events Will Occur

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**CFA Practice Question**

A survey of top executives revealed that 35% regularly read

*Time*magazine, 20% read*Newsweek*, and 40% read*U.S. News & World Report*. Ten percent read both*Time*and*U.S. News & World Report*. What is the probability that a particular top executive reads either*Time*or*U.S. News & World Report*regularly?A. 0.85

B. 0.06

C. 0.65

**Explanation:**35% + 40% - 10% = 65%

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**User Contributed Comments**
8

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

rgat |
where did 10% come from? |

capitalpirate |
10% reading both! |

Criticull |
you can't double count the intersection... |

Daddykay |
makes sense |

clipp |
formula: P(A or B) = P(A)+P(B) - P(AB) |

rjasins1 |
the probability of AB occuring together is 14% (.35 *.40). What am I missing? Thanks! |

myron |
@rjasins1: if the two events are independent, yes P(A and B) = P(A) * P(B). The question does not specify they are independent events. |

gyee2012 |
@clipp takes on the assumption that the magazines are independent events to get the answe |