- CFA Exams
- CFA Level I Exam
- Study Session 3. Quantitative Methods (2)
- Reading 9. Common Probability Distributions
- Subject 5. The Binomial Distribution

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**CFA Practice Question**

Suppose that 20% of all drivers come to a complete stop at an intersection having flashing red lights in all directions when there are no other cars visible. What is the probability that, of 15 randomly selected drivers coming to the intersection under these conditions, exactly 5 will come to a complete stop?

B. 0.188

C. 0.812

A. 0.103

B. 0.188

C. 0.812

Correct Answer: A

n = 15 and pai = 0.2, so p(5) = 15!/[5! x 10!] x (0.2)

^{5}x 0.8^{10}= 0.103.###
**User Contributed Comments**
12

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

aspazia |
calculating exactly the same thing i get 0.0968 ??? |

surob |
Check your calculation again. I got it right. |

aakash1108 |
0.103182294319104 - The exact answer. |

TammTamm |
These problems are super long. I hope there won't be any like this on the test. |

wundac |
actually this one is extremely short: 15 ncr 5 * .2^5 * .8^10 = .103 |

duongth307 |
@aspazia: The problem of your calculation is the rounding of .2^5. It is 0.00032 instead of 0.0003 |

Shammel |
@ duongth307: I kept getting .103 as well. However, I set my TI BA calculator to 5 decimal points and I got the right answer. How many decimal points do you guys recommmend setting a calculator to going into the exam? |

DonAnd |
I usually have mine set to 6 d.p. |

atemple315 |
I have mine set up on the 9 - it then extends where needed, but wont show unecessary dp. |

student111 |
factorial on BAII how ? |

johntan1979 |
Don't ever round. Learn to use the STO and RCL function of the calculator. |

davidmort |
How do you calculate on an HP12c |