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Natasha_4902
#1 Posted : Friday, July 03, 2020 6:10:39 PM
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Hi,

For questions asking about the probability/chance of certain conditions happening that are more complex than a punnet square could solve, how do you determine what number is the base and what number is the exponent?

For example, which expression gives the probability that a mother and father will have 4 children, 2 girls and 2 boys, in any birth order?

Is there a certain pattern we can use to solve these questions?

Thank you
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INSTR_Katerina_102
#2 Posted : Sunday, July 05, 2020 5:48:22 PM
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Hi,

Usually when I address these questions I try to use this kind of approach.

P = (# ways to desired result)/(Total # of ways)

Usually for this type of question total number of ways is convenient to access.

Here we have 4 children with 2 options of sex.

2*2*2*2 = 2^4 = 16 possible ways.


Therefore our P = (# of ways to 2B2G)/(Total # of ways)

For a larger dataset you might need more advanced math, but for this type of question and MCAT questions the math is generally simpler.

We can use the BBGG and count the number of ways to get this:

BBGG
GGBB
BGGB
GBBG
BGBG
GBGB

Getting a total of 6 ways to 2B2G.

This simplfies our P = 6/16 = 3/8 = 37.5 %

I think there are more elegant mathematical ways to do this, but I don't know them off the top of my head, nor do I know any particular patterns to this type of question.

I often find it more comforting on the MCAT to have written down some of my reasoning on scrap as if I have it as an abstract formula it's harder to check/recall when you are checking over questions.
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