CFA Practice Question

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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.

A. 0.063
B. 0.571
C. 0.273
Correct Answer: C

7C4 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:

.5[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!
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