FDP Extra Credit Data Sufficient Question

[jrsandigo]

I'm looking to better understand this DS problem:

An engine used up fuel at a constant rate
until it ran out of fuel. At what time did the
engine run out of fuel?
(1) At 1:00 P.M., the engine had 2/3 more fuel than it had at 5:00 P.M.
(2) At 1:00 P.M., the engine had 6 more
liters of fuel than it had at 5:00 P.M.

I've reviewed MGMAT's answer but still can't internalize it. Can I get some help and explanation?

Thanks!

[tim]

Before we help with this question, we'd you to show some effort of your own. What did you try on this question? Where did you get stuck? What problems did you have with our explanation?

[JustinS398]

Hi,

I interpreted this problem as insufficient because both statements state that the car had a certain amount of fuel "more" than the car did at 5PM. From the wording of the statements, the car has a more fuel at 1PM than 5 PM, but I could not see how to solve when the car would run out of fuel given that since there is no detail describing at what time the car had a full tank.

Reading this statement, am I supposed to assume that the car has a full tank at 1 PM? If so, then I understand the answer. If not, then I'm having trouble understanding.

[tim]

This problem does not require us to know how big the tank was at all. The fact that fuel is burning at a constant rate means that we can take the relative values of fuel at any two points in time and use that to extrapolate when the tank will be at 0. Please see the official explanation for more details if it is not clear exactly how to do this.

[RonPurewal]

Imagine a literal gas gauge. For statement 1, picture the gas gauge at two different levels--one of which is greater than the other by two-thirds. For instance, 3 gallons and 5 gallons. Or 6 gallons and 10 gallons. Etc.

Now, think about how fast the gas is running out. If you're the more visual type, you can think about how fast the gauge is running down, rather than thinking about literal numbers.

[JustinS398]

Thank you for the help. I think I understand. I just had a little trouble visualizing an exact time to empty since no values or tank level are specified. But after adding a variable x as a frame for reference at 5PM, and finding how x changes in 4 hours from its relationship to 1PM, I can determine how much more time it take to make x-->empty. I also plugged in some random numbers to prove the point, and it worked.

[tim]

Cool. Let us know if there are any more questions on this one.