an achiever probability question

[huk1985]

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What will be the likelihood of having exactly 1 boy in a family planning for three children?Answer is 3/8. I get that possible out comes are eight using the 2^3(two possible outcomes three times), but I don't get where 3 came from. Could someone explain how to get 3?

 

[Streetwolf]

What will be the likelihood of having exactly 1 boy in a family planning for three children?Answer is 3/8. I get that possible out comes are eight using the 2^3(two possible outcomes three times), but I don't get where 3 came from. Could someone explain how to get 3?

# of ways of choosing the kid that can be a boy is (3 choose 1) = 3. If you have no idea what I'm talking about, google 'math combination' and search for the term 'nCr'. Or browse around SDN a bit. Plenty of threads.

To just visualize it, if you had an oldest, middle, and youngest child, then any of those 3 could be the boy. That's where the 3 comes from.

 

[dentman82]

1/2 x 1/2 x 1/2 = 3/8 Just add the numerators to get 3.

 

[Streetwolf]

1/2 x 1/2 x 1/2 = 3/8 Just add the numerators to get 3.

What? You don't just randomly add numerators when you multiply. The 3 comes from the fact that you need to do (1/2)(1/2)(1/2) 3 times to get 1/8 + 1/8 + 1/8 = 3/8.

 

[huk1985]

oh, got it thanks. I was just confused because the answer solution had something 3!/2!=3.. and I was confused how that related to this problem.