When a certain car uses premium fuel, the car averages 12

Question

When a certain car uses premium fuel, the car averages 12 miles for every 1.5 gallons of fuel. When it uses regular fuel, it averages 22.4 miles for every 3.5 gallons of fuel. What is the percent decrease in the ratio of miles to gallons for the car when it uses regular over premium fuel?

A) 10.4%
B) 15%
C) 20%
D) 54%
E) 86 2/3%

lastochka · Answer

c? can it really be that sraightforward?

DaveforMBA · Answer

Need to get both rates with a base reference.
Since the premium numbers uses 1.5 gallons and the regular uses 3.5 gallons, we then need to figure out how many miles per GALLON.

With premium we have the equation
12mpg/1.5 gallons=(miles X)/1 gallon

Solving for X gives us 8 miles per 1 gallon

With Reguler we have the equation
22.4mpg/3.5=(miles X)/1 gallon

Solving for X gives us 6.4 miles per 1 gallon

Therefore we have a decrease from 8 to 6.4. 
To get the percent decrease we use the equation
8x=6.4
X=.80 or 80 percent.

When we went from 8 to 6.4, there was a reduction of 20%. 

So I'd say the answer is C.

DaveforMBA · Answer

Guys, I'm sure you know your stuff, but we are here to help one another in addition to challenging ourselves with questions. 

For the benefit of all, PLEASE post your answers in a manner that explains how you came to your answer.

We have to think of our postings as archival information. Others will follow, look at the question and understand the concepts better ONLY if we take the effort to post something worth looking at in our replies.

Explaining how you got your answer also helps you to increase your own understanding of the concepts being tested by the question.

This idea of ellaborating our answers has been reitterated time and time gain... let's try to keep our postings to the spirit of truly long lasting and helpful responses.

I like the fact that your trying to give a right answer to the question though so don't think that I'm harping on the fact that your not being a help at all. it's just that the greatest good comes out of GMATClub when we make the best possible initiatives to keep quality high. 

Thanks, and I'm sorry if it sounds like I'm harping on any of you. I think we just need to be reminded occasionally of the quality GMAT Club is trying to maintain and for newcomers to the board to understand this idea as well.

lastochka · Answer

It's a good point. I do try to exlain my answers most of the time (providing I got the time), unless the question is truly straight forward and Its doutful that people will miss it. 

At any case, you're right.

K_s_r · Answer

Anser C : 20%

12 Miles / 1.5 gallons ---> 8 Miles/ Gallon
22.4 Miles / 3.5 Gallons

With 3. Gallons of premium you can travel 28 miles

so Percenatge decrease is (100 - 22.4 / 28) /100 Percent = 20%

ian7777 · Answer

Nearly everyone got the right answer. It's C.

When a certain car uses premium fuel, the car averages 12

Prep Toolkit

Top 5 GMAT Debrief Videos

615 to 715 in 15 Days (Ria's Strategies)

More than Quant/Verbal Abilities: Speed vs. Accuracy

745 with Only Self-Prep and GMAT Club

From 555 to 765: 210-point Improvement

Perfect 805 Score Debrief by Julia

My Rewards