[X] Privacy Policy + T&C We use cookies to personalise our content and ads, and for traffic analysis. Information about your use of our site is shared with our advertising and analytics providers. You also agree to our T&C.

If a person has two children, and truthfully answers yes to the question "Is at least one of your children a girl?", what is the probability that both children are girls?

[Ref: ZRUZ]

If they had two children called A and B, before the answer to the question they could have been any one of the following:

A = boy  B = boy
A = boy  B = girl
A = girl B = boy
A = girl B = girl

After the answer, ONLY the first option can be ruled out. Of the remaining 3 options, only 1 of them means that they are both girls. QED.

NOTE: This is the correct and only answer. Probability is the topic that most often causes problems, as it's not always intuitive. There are lots of websites with probability tips and tricks to help you to understand why this answer is correct.

Back to the puzzles...

Top 10 Illusions

 Shadow Illusion Level Balance? Same Length Red Lines? Spinning Dancer Purple Nurple