I took the Dec. LSAT and have a question about one of the questions. There was a LR question which stated that the value of a postage stamp depended on its rarity and its age, then said that a given stamp had a printing error and was old and so must be valuable. The question was to select which assumption must be valid in order to properly draw the conclusion that the stamp was valuable. Two of the options were (paraphrased):
a) Being old makes a stamp more valuable
b) Printing errors are rare
I selected a, and the credited response was b. Am I mistaken in thinking that both a and b are necessary for this argument to work? For example, replace "postage stamp" with car. Cars in general are more valuable when new, although some classic old cars are much more valuable now than they were when new. Age is one of the most important factors in a carīs value, but that does not provide information as to how they correlate. Something similar could be true for postage stamps. If the question were to identify the assumption that most strengthens the conclusion then I could see crediting b but not a, but since the question asked which assumption would allow the conclusion to be properly drawn, I donīt think either a or b are correct answers since both of them are necessary.