Ok, this is another problem that was kind of lame as worded but could be turned into a useful example
Problem as stated: Suppose that 3% of births give rise to twins. What percentage of the population is a twin 3%, less than 3%, or more that 3%.
So the problem is obviously trying to get the reader to realize the birth of twins increases the population by two people as opposed to “normal” births increasing the population by a single person. Then intuit what that means to the percentage of twins in the population.
No reason that the reader should not be able work out the exact percentage given the problem as stated and the assumption that triplets, quintuplets, and all other multiple births are a negligibly small percentage of the population.
Stated this way I can use this problem to introduce readers to the idea of taking two equations dependent on some third and unknown variable that cancels out later.
