Practice GMAT Data Sufficiency Question
Return to the list of practice GMAT data sufficiency questions.
Peter can drive to work via the expressway or via the backroads, which is a less delayprone route to work. What is the difference in the time Peter would spend driving to work via the expressway versus the backroads?
 Peter always drives 60mph, regardless of which route he takes; it takes Peter an hour to drive roundtrip to and from work using the backroads
 If Peter travels to and from work on the expressway, he spends a total of 2/3 of an hour traveling
Correct Answer: C
 Since this is a distanceratetime problem, begin with the core equation:
Distance = Rate(Time)
Note that there are two distance equations, one for traveling the expressway and the other for traveling the backroads.
Distance_{express} = Rate_{express}(Time_{express})
Distance_{backroad} = Rate_{backroad}(Time_{backroad})  In order to answer the question, you need to find the value of:
Time_{express}  Time_{backroad} 
Evaluate Statement (1) alone.
 Statement (1) says Rate_{express} = Rate_{backroad} = 60 mph.
 Statement (1) also says that 2(Time_{backroad}) = 1 hour
(Time is multiplied by 2 because the statement gives the time "to drive roundtrip to and from work.")
Time_{backroad} = 1/2 hour.  Filling in all the information, you have the following:
Distance_{express} = 60(Time_{express})
Distance_{backroad} = 60mph((1/2) hour) = 30 miles  Without information concerning the distance or time to travel on the expressway, you cannot solve for Time_{express}. Consequently, Statement (1) is NOT SUFFICIENT.

Evaluate Statement (2) alone.
 Statement (2) says that 2(Distance_{express}) = Rate_{express}((2/3) of an hour)
(Note that the distance is multiplied by two because Peter travels twice the distance when he goes "to and from work".)
So, Time_{express} = 1/3 of an hour.  Fill in the information that is known:
Distance_{express} = Rate_{express}(1/3 of an hour)
Without any information about Time_{backroad}, you cannot determine Time_{express}  Time_{backroad}. Statement (2) is NOT SUFFICIENT.
 Statement (2) says that 2(Distance_{express}) = Rate_{express}((2/3) of an hour)

Evaluate Statements (1) and (2) together.
 Putting Statements (1) and (2) together, you know Time_{backroad} from Statement (1) and you know Time_{express} from Statement (2).
 So, Time_{express}  Time_{backroad} = 1/3hour  1/2hour or 20 minutes  30 minutes = 10 minutes or 1/6 of an hour. Statements (1) and (2) together are SUFFICIENT.
 Since Statement (1) alone is NOT SUFFICIENT and Statement (2) alone is NOT SUFFICIENT yet Statements (1) and (2), when taken together, are SUFFICIENT, answer C is correct.
Return to the list of practice GMAT data sufficiency questions.