Kim purchased 20 gallons of gas. She paid for 10 + 0.9*10 = 19 gallons, so the overall discount she got was 1/20 = 5%.

Isabella purchased 25 gallons of gas. She paid for 10 + 0.9*15 = 23.5 gallons, so the overall discount she got was 1.5/25 = 6%.

6 is 6/5*100 = 120% of 5.

Answer: D.
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Hi Bunuel,

Thanks for the explanation. A small clarification required though..

You have applied the specified discount on #Units of Gallons. Though it doesn't matter but I chose to look at the given discount in terms of Price/Gallon ($1/G) and then followed the same approach.

I usually take time on percent questions if they're of 700+ level. Do you see any obvious flaw in my approach? I could work on some particular concept files if you think that may help me provide a direct and efficient approach to percent problems. Accuracy is moderate on higher level percent question but time is of concern. This includes my accuracy on Manhattan CATS.

Hari






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Please refer to the discussion above.
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Let’s assume that the price per gallon of gas is $10. Thus, the discounted price per gallon of gas after the first 10 gallons is 0.9 x 10 = $9. In other words, after the first 10 gallons, each additional gallon has a $1 discount in price.

Now let’s calculate the total discount for each person. Since Kim purchased 20 gallons of gas, the 10 additional gallons (that is, after the initial 10 gallons) will receive a $10 discount, so her total per-gallon discount is 10/20 = $0.50. Since Isabella purchased 25 gallons of gas, the 15 additional gallons (that is, after the initial 10 gallons) will receive a $15 discount, so her total per-gallon discount is 15/25 = $0.60. Therefore, Isabella’s total per-gallon discount is 0.60/0.50 = 6/5 = 1.2 = 120% of Kim’s total per-gallon discount.

Answer: D
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Let the cost of fuel be $10 per gallon.
Kim
First, 10 gallons price=10*$10=$100
2nd 10 gallon Price=10*$9=90 (Discount of 10% or $1 after first 10 gallons)
Total Paid $190
In case there would have been no discount than amount paid would have been $200(20*10)
Savings $10.
Total savings on Total fuel purchased=\(\frac{10}{20}\)=\(\frac{1}{2}\)
Isabella
First 10 gallon price=10*$10=100
2nd 15 gallon Price=15*$9=135 (Discount of 10% or $1 after first 10 gallons)
Total Paid $235
In case there would have been no discount than amount paid would have been $250(25*$10)
Savings $15.
Total savings on Total fuel purchased=\(\frac{15}{25}\)=\(\frac{3}{5}\)

% of \(\frac{Isabella}{Kim}\)= \(\frac{3}{5}\)÷\(\frac{1}{2}\)=\(\frac{6}{5}\)=1.2*100=120%