Logical reasoning PrepTest 129 · Section 3 · Question 10

Incorrect. The conclusion is that bicyclists are "at least partially responsible" for these accidents, so motorists could be responsible, as well.

Incorrect. The premises are causal, so there's no jump from correlation to causation.

Correct. Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Errors in Reasoning

Stimulus Summary:
25+% of bike accidents are at least partially caused by bicyclists failing to obey traffic laws.
25+% of bike accidents are at least partially caused by bicyclists not wearing their safety equipment.
Therefore: Bicyclists are at least partially responsible for over 50% of bike accidents.

Answer Anticipation:
The conclusion is about responsibility, so our first step should be to check the details to see if the group concluded to be responsible can be said to be responsible based on their actions. And in both scenarios outlined, they can be—either by failing to obey laws, or by failing to wear appropriate safety gear. This common flaw—concluding someone is responsible for something out of their control—isn't present here.

Next, since the argument mentions percentages, we should check to see if there's a jump between that and amounts. However, the conclusion isn't about the number of bike accidents, but rather the percentage of bike accidents ("more than half" is over 50%), so there's no flaw there.

The last place we can look is in thinking about these accidents as sets, and consider whether we can add them together, or if it's possible that they overlap. If most of those accidents that are at least partially caused by failure to obey traffic laws are also at least partially caused by a lack of safety equipment, then the percentages can't be added together, as you're essentially double-counting some of the accidents. And, in this case, that could very well be the case. Both types of accidents note the causes as being "a factor," not the only factor, in these accidents, and it's possible a bicyclist could fail to signal to turn while also not wearing a helmet. This argument treats the two 25+% accident groups as separate, but they could overlap and thus make up under 50% of all bike accidents.

Answer Explanation:
This answer highlights that the argument tries to "add" two types of accidents together to get a total rate, when it doesn't show that each type of accident is distinct. If 90% of accidents where the bicyclist didn't obey traffic laws also saw the bicyclist not use adequate safety equipment, then these groups don't add up to over 50% because those 25%s overlap quite a bit.

Key Takeaway:
Whenever an argument tries to add things together, see if the things being added are distinct. If there could be overlap, then they can't be added, since you'd be double-counting some elements.

Incorrect. Unless there's a specific reason to doubt cited figures, there's no need on the LSAT to cite the source. Remember, on the LSAT, you're expected to treat the premises as true—no citation required.

Incorrect. The argument never discusses accident severity or injuries, so this answer is out of scope. If the argument had jumped between accidents to serious accidents, or accidents where someone was seriously injured, then this answer might be a consideration.