I think this one is E. The x's don't cancel out becuase they are not necessarily the same number.... X1970 does not equal X1980 and, therefore, they cannot be cancelled out. We can't solve this even with both statements becuase we don't know anything about the median income in country X. So, even though we know how Y relates to X in 1970 and how Y relates to X in 1980, without knowing anythign about the two different values of X, we cannot know the overall change in Y.
For example, say that in 1970 median income in X was 300,000 and in Y was 200,000. This satisfies Statment (1). Then, if median income in X rises to 350,000 in 1980, Statement (2) would tell us that median income in Y is 175,000, which would be a decrease of 12.5%.
However, if median income in country X fell from 300,000 to 250,000 from 1970 to 1980, Statement (2) would imply that median income in country Y would be 125,000 in 1980, which would be a decrease of 37.5%.
Without knowing how X changes, knowing how Y compares to the two different values of X does allow us to determine the actual change in the value of Y.
For example, say that in 1970 median income in X was 300,000 and in Y was 200,000. This satisfies Statment (1). Then, if median income in X rises to 350,000 in 1980, Statement (2) would tell us that median income in Y is 175,000, which would be a decrease of 12.5%.
However, if median income in country X fell from 300,000 to 250,000 from 1970 to 1980, Statement (2) would imply that median income in country Y would be 125,000 in 1980, which would be a decrease of 37.5%.
Without knowing how X changes, knowing how Y compares to the two different values of X does allow us to determine the actual change in the value of Y.
