Thank you for your question. There are two different categories of information at issue in the stimulus for this errors in reasoning question. First, luggage that contains NO explosives. We are told that only 1% of luggage with NO explosives will trigger the scanner. Fine.
The second category of information is regarding luggage that DOES contain explosives. The conclusion of this stimulus is that 99% of luggage WITH explosives will trigger the scanner.
This conclusion is flawed. A premise about luggage with NO explosives cannot establish a conclusion about lugged that DOES contain explosives.
Answer choice (E) says exactly this (albeit in a classically obscure LSAT way). The argument is flawed because the conclusion substitutes one group (luggage with NO explosives) for a different group (luggage WITH explosives) in the statement of a percentage.
Hope this helps! Please let us know if you have any additional questions.
