Multiple choice general knowledge math & puzzles

Ronald and Michelle have two children. The probability that the first child is a girl, is 50%. The probability that the second child is a girl, is also 50%. Ronald and Michelle tell you that they have a daughter. What is the probability that their other child is also a girl?

  1. 2by3

  2. 1by3

  3. 3by3

  4. 4by3

Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

This is the Boy or Girl paradox. The possible gender combinations for two children are BB, BG, GB, GG. Knowing at least one is a girl eliminates BB. Of the remaining 3 (BG, GB, GG), only 1 is GG. Thus, the probability is 1/3.