This is a moderately difficult question on the concept of percentages. Because it is a ‘Could be’ kind of a question, the strategy here will be to take simple cases and try to prove each statement true, ONCE.
You can also adopt the minimization and maximization approach and see how many of the percentage values fall between the bounds. Let us look at both the approaches.
In 1990, the annual salaries of the clerks ranged from $40000 to $55000. In 2000, the annual salaries of the clerks ranged from $70000 to $110000.
If we consider the annual salaries in 1990 as $40000 and in 2000 as $80000, the percentage increase will be 100%. So, statement II could be a possible percentage increase. Therefore, options A and can be ruled out since they say only I statement could be true/only statement III could be true, which of course is wrong.
If the annual salaries in 1990 were $40000 and they were $10000 in 2000, the percentage increase will be 150%. So, statement III could be a possible percentage increase. Therefore, we can eliminate option B now.
If the annual salaries in 1990 were $50000 and were $75000 in 2000, the percentage increase would be 50%. So, statement I also could be a possible percentage increase.
Therefore, the correct answer option HAS to be E.
The other approach is to look at what could be the minimum and the maximum percentage increases possible.
For the minimum percentage increase, we have to take the biggest value of the salaries in 1990 and the smallest value of the salaries in 2000 i.e. $55000 to $70000. This is a percentage increase of approximately 27%.
For the maximum percentage increase, we take the smallest value in 1990 and the biggest value in 2000 i.e. $40000 to $11000. This is a percentage increase of 175%.
Clearly, all the percentage values given in the statements are in this range and therefore all of them could be the percentage increases.
Obviously, each method has its own merits. The value method is simple and quick, but only if you are able to figure out the values like the ones shown above. The conceptual method may seem more convincing to the purist in you. Regardless of the method that you adopt, this question should take you about a minute and a half, to come out with the right answer.
Hope this helps!