- CFA Exams
- CFA Exam: Level I 2021
- Study Session 3. Quantitative Methods (2)
- Reading 9. Common Probability Distributions
- Subject 5. The Binomial Distribution

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**CFA Practice Question**

Find the probability of having exactly four girls in seven births. Assume no multiple births and that male and female births are equally likely and independent.

B. 0.571

C. 0.273

A. 0.063

B. 0.571

C. 0.273

Correct Answer: C

_{7}C_{4}x (0.5)^{4}x (0.5)^{(7-4)}= 0.273###
**User Contributed Comments**
15

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

kevin77cfa |
How do I do 7C4 on Calculator BA II. |

JonRagati |
2nd -> + |

olagbami |
press d ffg: 7,2nd,+,4,= |

tanak |
What about HP12c for 7C4 |

azramirza |
How would u know this is binomial theorm..u can also do a simple prob of 4/7=0.571??? please help?? |

Jurrens |
azramirza: seems logical, but think of this way: since each birth is independent, there is a 50% chance of each birth. Remember the quarter problem in the notes, this example is no different (with exception to heads being a boy and tails being a girl). Knowing this, it gives a new perspective of just the simple fractional solution. |

jorgeman81 |
guys please help me, in the BA II plus I input: 7,2nd,+,4 and I get 35, what I am doing wrong? |

jorgeman81 |
oh! got it! |

amyjones |
I can't figure this out on the HP12c |

johntan1979 |
Dichotomous... 2 outcomes... 2 categories... Definitely a binomial/Bernoulli question |

Callie2 |
HP12c: 7[g][3]7[enter]4[-][g][3]4[g][3][x][/] .5[enter]4 [yx][x] 1[enter].5[-]7[enter]4[-][yx][x] |

Shaan23 |
for super duper fun you can do it without binomial. total ways you can have MMMFFFF is 7C4. In denominator how many ways can you do it ---> 2^7. so 7C4 / 2^7 ----> same answer.. |

Yrazzaq88 |
BA Plus: 7 [NcR] 4 = 35 (35 x .5^7) =.273 We multiply by .5 because it says, "Male and Female are equally likely." We choose 7 because we have 7 total births. |

Rachelle3 |
4 divided by 7 = 0.571428571 what is all this!!! |

Rachelle3 |
so obviously not b right haha! |