GMAT Practice Question (One of Hundreds)
Peter can drive to work via the expressway or via the backroads, which is a less delay-prone 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 round-trip 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
Translate the information into the equation: distance = rate(time). Plug in as much information as you can in each statement and see if you can Texpress - Tbackroad.
- Since this is a distance-rate-time 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.
Distanceexpress = Rateexpress(Timeexpress)
Distancebackroad = Ratebackroad(Timebackroad)
- In order to answer the question, you need to find the value of:
Timeexpress - Timebackroad
Evaluate Statement (1) alone.
- Statement (1) says Rateexpress = Ratebackroad = 60 mph.
- Statement (1) also says that 2(Timebackroad) = 1 hour
(Time is multiplied by 2 because the statement gives the time "to drive round-trip to and from work.")
Timebackroad = 1/2 hour.
- Filling in all the information, you have the following:
Distanceexpress = 60(Timeexpress)
Distancebackroad = 60mph((1/2) hour) = 30 miles
- Without information concerning the distance or time to travel on the expressway, you cannot solve for Timeexpress. Consequently, Statement (1) is NOT SUFFICIENT.
Evaluate Statement (2) alone.
- Statement (2) says that 2(Distanceexpress) = Rateexpress((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, Timeexpress = 1/3 of an hour.
- Fill in the information that is known:
Distanceexpress = Rateexpress(1/3 of an hour)
Without any information about Timebackroad, you cannot determine Timeexpress - Timebackroad. Statement (2) is NOT SUFFICIENT.
Evaluate Statements (1) and (2) together.
- Putting Statements (1) and (2) together, you know Timebackroad from Statement (1) and you know Timeexpress from Statement (2).
- So, Timeexpress - Timebackroad = 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.