The public service advertising campaign promoting the use of helmets

KAPLAN OFFICIAL EXPLANATION:

STEP 1: IDENTIFY THE QUESTION TYPE
The question stem alerts you to the idea that this argument is flawed, so Flaw is definitely the question type here.

STEP 2: UNTANGLE THE STIMULUS
The author concludes that the number of broken-bone bicycle injuries has gone up from last year to this year. The evidence for this is that broken bones made up 20 percent of this year’s total bicycle-related injuries but were only 14 percent of last year’s total.

STEP 3: PREDICT THE ANSWER
As soon as you see both percentages and numbers mentioned in the stimulus for a Flaw question, beware. In the Quantitative section, you will learn, if you have not already, that you must be careful when working with percentages. Twenty percent is guaranteed to equal a higher number than 14 percent only if those percentages are of the same total. And since the total number of injuries is much lower this year than last year, 20 percent of a much lower total could actually equal a lower number than 14 percent of last year’s higher total. If you’re having trouble seeing this, you can use the Quant strategy of Picking Numbers. Suppose there were 100 bicycle injuries last year. That means that 14 percent, or 14 total, of those injuries involved broken bones. You know that this year, injuries have been reduced by 70 percent. In this example, that means there were a total of 30 bicycle injuries this year. Twenty percent of the new, lower total is 6 broken-bone injuries, a significantly lower number than last year’s 14. The flaw here is the author’s assumption that an increase in percentage cannot be consistent with a decrease in actual number.

STEP 4: EVALUATE THE CHOICES
Only (D) accurately captures the logical flaw in this argument—confusing percent and actual value. (D) is the correct answer. The fact that the author mentions only two types of injuries, as (A) says, is not a flaw in the argument, which concerns only whether or not the number of broken bones has been reduced. Other types of injuries are irrelevant. Since two sets of causes aren’t discussed, you can rule out (B). Causation does figure in many GMAT flaws, but not this one. (C) might seem tempting, since it does relate to the “percentage versus actual number” issue, but if the total number of bicyclists increased over the past year, the reduction in the number of total injuries would actually be greater. And since a 70 percent overall decrease in injuries could, in fact, allow for an 85 percent decrease in one specific type of injury, (E) can be ruled out as well.