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During a special promotion, a certain filling station is off

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During a special promotion, a certain filling station is off

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During a special promotion, a certain filling station is offering a 10 percent discount on gas purchased after the first 10 gallons. If Kim purchased 20 gallons of gas, and Isabella purchased 25 gallons of gas, then Isabella‟s total per-gallon discount is what percent of Kim‟s total per-gallon discount?

(A) 80%

(B) 100%

(C) 116.7%

(D) 120%

(E) 140%

OA D

Source: Princeton Review

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Not too sure about this approach... but..
Let P be the price per gallon
Kim = 10P+0.9(10P) = 19P (versus 20P originally)
Isabelle = 10P+0.9(15P) = 22P (versus 25P originally)

Thus Kim has a discount of $$\frac{1}{20}P$$
Isabelle has a discount of $$\frac{3}{25}P$$

This corresponds to 5% discount for Kim and 12% discount for Isabelle

Next to calculate the % of Isabelle's discount in terms of % Kim's discount
$$\frac{12-5}{5}$$

Which gives us 140%

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Hi All,

We're told that during a special promotion, a certain filling station is offering a 10 percent discount on gas purchased AFTER the first 10 gallons. Kim purchased 20 gallons of gas, and Isabella purchased 25 gallons of gas. We're asked for Isabella's total PER-GALLON DISCOUNT as a percent of Kim's total PER-GALLON DISCOUNT. This question can be approached in a couple of different ways, including by TESTing VALUES.

To start, let's set the price at $1 for 1 gallon gallon of gasoline.

Kim purchased 20 gallons, with the last 10 gallons discounted 10%, meaning that she saved (10)($1)(.1) = $1.00 off of 20 gallons
Isabella purchased 25 gallons, with the last 15 gallons discounted 10%, meaning that she saved (15)($1)(.1) = $1.50 off of 25 gallons

Kim's per-gallon discount is 1/20 = .05; Isabella's per-gallon discount 1.5/25 = 3/50 = .06

Thus, the percent would be .06/.05 = 6/5 = 1.2 = 120%

Final Answer: D

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

_________________
Contact Rich at Rich.C@empowergmat.com

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