I realize this may seem petty, but this is roughly like calculating the chance of picking the three of clubs as a random card from a deck is one in fifty. It’s close, but it’s wrong. An implicit assumption otherwise seems misguided; it should be made explicit (to make a logic problem rather than a logic and biology problem.)
You are right to point that out. I think that the spirit of the question assumes equal probability of 50% B,G for each birth independent of previous births and statistics in order to make it a probability and logic question, and not one of biology.
wgd is correct as to the logic, but not as to the biology of the problem. In fact, the other kid is more likely than not to be male.
These problem types tend to assume an equal chance of a boy and a girl being born, which is a false assumption. (See: http://www.infoplease.com/ipa/A0005083.html)
I realize this may seem petty, but this is roughly like calculating the chance of picking the three of clubs as a random card from a deck is one in fifty. It’s close, but it’s wrong. An implicit assumption otherwise seems misguided; it should be made explicit (to make a logic problem rather than a logic and biology problem.)
You are right to point that out. I think that the spirit of the question assumes equal probability of 50% B,G for each birth independent of previous births and statistics in order to make it a probability and logic question, and not one of biology.