Probability Help

[sammy1245]

I have a test coming up and I don't really understand it.

I'll take 2 questions out of my math book to use as examples, then you could explain them to me.

In a family of 2 kids, excluding multiple births, what is the probability of having 2 girls?

In a family of 3 kids, excluding multiple births, what is the probability of having 2 boys and 1 girl in any order?

Thanks!

 

[chrisr]

To answer, you can write down the "possibilities".

2 kids could be 1 boy, 1 girl or 2 boys or 2 girls. That way it "looks like" 3 possibilities.
If a boy or girl are "equally likely" to be born,
how many different possibilities are there?

The birth orders could be boy girl or boy boy or girl boy or girl girl.
The probability of having 2 girls is how many chances from the total?

 

[papermate2004]

The probability of a girl is 50/50
The probability of another girl is 50/50

Multiply the probabilities together to find the probability of two girls: .5*.5=.25 or 25% chance of two girls

For two girls and a boy
p(girl): 50/50
p(girl): 50/50
p(boy): 50/50

Multiply again: .5*.5*.5= .125 or 12.5% chance of two girls and a boy

Remember:
Each trial is independent and equally as likely