GMATD11 wrote:

While driving on the expressway, did Robin ever exceed the 55-miles-per-hour speed limit?

(1) Robin drove 100 miles on the expressway.

(2) Robin drove for 2 hours on the expressway.

NOTE: There's nothing here to suggest that

Robin's speed was constant. Sure, she MIGHT have traveled at a constant speed, or her speed may have varied throughout the trip.

Target question: Did Robin's speed ever exceed 55 miles per hour? Statement 1: Robin drove 100 miles No information about Robin's travel TIME so statement 1 is NOT SUFFICIENT

Consider these two possible scenarios that yield conflicting answers to the

target question:

Case a: driving at a constant speed, Robin spent 1 hour driving 100 miles, in which case her speed was 100 miles per hour. So,

Robin's speed DID exceed 55 miles per hourCase b: driving at a constant speed, Robin spent 10 hours driving 100 miles, in which case her speed was 10 miles per hour. So,

Robin's speed did NOT exceed 55 miles per hourSince we cannot answer the

target question with certainty, statement 1 is NOT SUFFICIENT

Statement 2: Robin drove for 2 hours No information about the DISTANCE Robin traveled. So, statement 2 is NOT SUFFICIENT

Consider these two possible scenarios that yield conflicting answers to the

target question:

Case a: driving at a constant speed, Robin spent 2 hours driving 1000 miles, in which case her speed was 500 miles per hour. So,

Robin's speed DID exceed 55 miles per hourCase b: driving at a constant speed, Robin spent 2 hours driving 2 miles, in which case her speed was 1 mile per hour. So,

Robin's speed did NOT exceed 55 miles per hourSince we cannot answer the

target question with certainty, statement 2 is NOT SUFFICIENT

Statements 1 and 2 combined Consider these two possible scenarios that yield conflicting answers to the

target question:

Case a: driving at a constant speed, Robin spent 2 hours driving 100 miles, in which case her speed was 50 miles per hour. So,

Robin's speed did NOT exceed 55 miles per hourCase b: Robin drove 99 miles (at a constant speed) for 1 hour, and then spent 1 hour driving the remaining 1 mile. So,

Robin's speed DID exceed 55 miles per hour (during the 1st hour)Since we cannot answer the

target question with certainty, the combined statements are NOT SUFFICIENT

Answer: E

Cheers,

Brent

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Brent Hanneson – GMATPrepNow.com