Oz's Question of the day #219 (19/2/10) Maths !

[OZXJR]

My wife and I have have two children.
The probability that the first child is a boy, is 50%.
The probability that the second child is a boy, is also 50%.
I will tell you that one child is a boy.

What is the probability that our other child is also a boy ?.

PM answers please.

 

[k1c]

PM coming halfway

 

[Fz6Sa]

Pm Sent :cheer:

(Even though I haven't had much Math-Friday luck lately, just gotta keep trying I guess :thumbup

 

[discgolfdude]

pm has been sent

 

[SirIsaac]

Probability PMed.

 

[Kazza]

PM on its way

 

[Coopdman]

99% probability my PM was sent

 

[chaskell27]

PM on the way :thumbup:

 

[Discofrank]

100% i have no idea!

and 100% NO pm

 

[Live4Snow]

PM sent to ya.

:thumbup:

 

[Less]

PM sent late today.

 

[Stevenator]

PM Sent... this hangover is killing me... :beer:

 

[krid80]

Probably pm'd

 

[teej21012]

Pm sent....

 

[ELIZABETH]

PM in your PM box

 

[Senior]

PM'd my correct (fingers crossed) answer with an explanation . . .

bit late in the day as I've not been at work and this is my first time at a PC today

(better be right after blowing my trumpet)

 

[Chris]

PM sent! =)

 

[CHEMIKER]

PM'd my guess. Probability of my guess being right: 0

 

[OZXJR]

Answer:33%

Rep and casino cash winners:Fz6sa and Coopdman

Nicely worked out guys.

Here is Coops answer .

First Child______Second Child
Boy_______________Boy
Boy_______________Girl
Girl_______________Boy
Girl_______________Girl <-- not possible

So we have a total of 3 possibilities. Taking the known boy out of the equation we see the options become, (Boy, Girl, Girl).

So the probability that you have a second boy is 1 in 3, or 33.333333333%

 

[teej21012]

I'm going to have to disagree. By using Coop's exact logic, order of children is irrelevant (i.e. boy-girl is the same as girl-boy). That reduces it to only two choices which is boy-boy or the combination of boy-girl/girl-boy. This is not a permutation. Had the problem stated that the first child was a boy, then Coop's logic would hold true. All it says is one child is a boy.