I've found this video about conditional probability:(adsbygoogle = window.adsbygoogle || []).push({});

All steps look correctly, but the result does not make any sense.

I'm ok with the part about frogs, but not so with the boy/girl computation.

To sum it up:

1) I have two children and at least one of them is a boy. What is a probability I have a girl?

Answer: 2/3

2) I have two children and at least one of them is a boywho was born on Tuesday. What is the probability I have a girl?

Answer: ~52%

It does not make any sense... to me anyway.

Whatever day of week I say, it tells you nothing about the boy/girl status, does it?

If I said the boy was born on January 1, 2001, would it shift the probability even closer to 50%? How is that possible?

----------

If you don't want to watch the video:

1) out of the 4 equally probable possibilities ##BB##, ##BG##, ##GB##, ##GG##, the ##GG## is crossed out, leaving 2 of 3 cases containing G.

2) out of the 14^2 equally probable cases ##B_{Monday}B_{Monday}## .. ##G_{Sunday}G_{Sunday}##, we have:

7 cases ##B_{Tuesday}B_{any}##,

6 cases ##B_{not\ Tuesday}B_{Tuesday}##

7 cases ##B_{Tuesday}G_{any}##,

7 cases ##G_{any}B_{Tuesday}##.

So, to have a G, we have (7+7)/(7+6+7+7)=14/27 ~ 52%.

**Physics Forums | Science Articles, Homework Help, Discussion**

Dismiss Notice

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# B Boy/girl riddle (conditional probability)

Tags:

Have something to add?

Draft saved
Draft deleted

Loading...

**Physics Forums | Science Articles, Homework Help, Discussion**