I think this one is harder than 600-700. Aren't you?
In a certain population, the two most heavily diagnosed diseases are schistosomiasis and malaria. Over the past five years, malaria has accounted for more than half of all disease cases, and schistosomiasis, which accounted for 40% of all disease cases in the community five years ago, accounted for 30% in the past year.
Schistosomiasis, malaria: main diseases.
Which of the following must be true on the basis of the statements above?
A. There were fewer cases of schistosomiasis last year than five years ago.
Percentages are not equivalent to absolute number. Misleading.
B. The percentage of disease cases from malaria has increased over the past 5 years.
Not really. The percentage given for malaria is the arithmetic average for the last 5 years. I.e. the percentages for each year could be manipulated greatly without changing the mean.
C. Some disease has experienced an increase in the number of its total cases, as long as the total number of disease cases went down by a number less than 30%.
Can be true, but doesn't have to. This 30% is really confusing here, but it's a red herring. Don't let it possess your mind.
D. Each year over the past five, malaria has accounted for a larger percentage of disease cases than schistosomiasis.
False for the same reason as B.
E. If the total number of schistosomiasis cases increased over the past five years, then the total number of disease cases must have increased by more than 30%.
Percentage value decreased. If the total number increased concurrently, then the total number of diseases had to increase even more. Count the given 30% if you have time on the GMAT, it's not necessary after all. Correct.
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