This is a simple problem. Consider you are the only chick that matters, and construct a table to say whether YOU get pecked. Your chance of being pecked comes down to only 4 outcomes. (1) YES - pecked twice. (2) YES - pecked from left wing only. (3) YES - pecked from right wing only. (4) NO - unpecked. The table has 4 elements, all of equal probability, 1 of which is unpecked. YOU are therefore pecked 3:1 ratio or 3:4 opportunities 75% of the time. For convenience, this needs to be conducted for 100 trials of YOU, and the answer is that 25 times YOU will NOT be pecked. The circular nature of the 100 chicks says that YOU are not unique, and your experience is the same as the others, so we extrapolate your experience of 100 trials to a single trial of 100 chicks just like YOU. 25 unpecked chicks, 50 get pecked once, 25 get double pecks.
This is the same table constructed for 100 women having two children and asking how many have no girls.
