Solutions

FALSE: The theoretical ratio can be different from the observed value -- that is natural random fluctation. If a coin is fair and has 50% probability of coming up heads, it does not mean that in 10 trials there will be exactly 5 heads. What it does mean is that the proportion of heads should be CLOSE to 50% and also this closeness should INCREASE as the sample size grows larger. The observed ratio will never EXACTLY equal the true probability.

SOME of the reasons why the MODEL might not match REALITY are the following:

1. The probability of boys birth may be slightly different from 50%
2. If parents decide to control births, and abort baby girls, while having baby boys, this can cause severe difficulties with the model,.
3. If cultural customs are such that baby girls are not given necessary medical care or nutrition, and sons are preferred, this would invalidate the model predictions