Problem Solving

Hi NansishSS,

We're told several facts about a car driving on a straight road:
1) The car drives at 1 mile/minute
2) The car uses 5 gallons of fuel every 2 hours
3) The car used exactly 3.75 gallons of fuel

We're asked to find the number of miles that the car traveled. This is essentially a 'rate' question - and you can do the 'math' in a few different ways (depending on how you want to organize the information.

We know that 5 gallons of fuel is used every 2 hours, so we can figure out how long 3.75 gallons of fuel will last:

(3.75/5)(2 hours)

7.5/5 hours = 1.5 hours = (1.5)(60 minutes) = 90 minutes

Since the care traveled 1 mile/minute, and the fuel lasted for 90 minutes, the car traveled 90 miles.

Final Answer: E

GMAT assassins aren't born, they're made,
Rich

NandishSS wrote:During a certain time period, Car X traveled north along a straight road at a constant rate of 1 mile per minute and used fuel at a constant rate of 5 gallons every 2 hours. During this time period, if Car X used exactly 3.75 gallons of fuel, how many miles did Car X travel?
A. 36
B. 37.5
C. 40
D. 80
E. 90

Since the car has a constant rate of 1 mile per minute, we can let r = the rate of the car in miles per hour and create the following equation:

1/1 = x/60

x = 60 mph

Since the car uses 5 gallons of fuel every 2 hours, we can let x = the number of hours driven when the car uses 3.75 gallons of fuel and create the following proportion:

5/2 = 3.75/x

5x = 7.5

x = 1.5 hours

We know that the rate of the car is 60 mph and the car has been driven for 1.5 hours; thus, the distance driven is 60 x 1.5 = 90 miles.

Alternate Solution:

Since the car uses 5 gallons of fuel every 2 hours, or 120 minutes, we can let x = the number of minutes when the car uses 3.75 gallons of fuel and create the following proportion:

5/120 = 3.75/x

5x = 120(3.75)

x = 90

So, the car is driven for for 90 minutes. Since it travels 1 mile per minute, it will have traveled 90 miles.

Answer: E