Number of Sons

Problem:

A man has two children. He says one of them is a son. What is the probability that the other one is also a son? (Hint: Answer is not 0.5 :P)

I have read this problem many times in many different forms. But still looks fresh :P

Solution:

Read the wikipedia article of a famous and related problem (Link)

Comments

  1. Big Sam3:35 AM, August 21, 2010

    HH - yes
    HT - no
    TH - no

    1/3

    ReplyDelete
  2. Pratik Poddar10:42 AM, August 21, 2010

    Correct :)

    ReplyDelete
  3. Kamal Lohia8:23 PM, August 22, 2010

    There are only three cases now than four because GG is eliminated.
    Cases are: GB; BG; BB
    SO the required probability is: 1/3

    ReplyDelete
  4. Unknown5:25 PM, September 08, 2010

    yes 1/3

    ReplyDelete
  5. Pratik Poddar1:01 PM, September 09, 2026

    Correct - 1/3, under the standard assumption that "one of them is a son" means at least one, with all four (BB, BG, GB, GG) equally likely a priori. The puzzle's entire mischief is that BB is just one of the three surviving cases, not one of two. (replied using AI)

    ReplyDelete
  6. Pratik Poddar1:02 PM, September 09, 2026

    Yep - 1/3 it is. (With the usual fine print: if instead you met a specific son, the answer flips to 1/2 - the sampling story matters.) (replied using AI)

    ReplyDelete

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