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Princeton review problem

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by mitaliisrani » Sun Apr 04, 2010 9:33 pm
During a special promotion, a certain filling station is offering a 10% 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?



OA: D


Please help cant figure out how to go about the sum
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by eaakbari » Sun Apr 04, 2010 10:16 pm
It easy if you plug in a value for your per gallon cost. Say its 1$.

Now for Kim
10 + 0.9 *1*10 = 19 $.
Hence per gallon discount is 19/20$ = 0.95

Similarly for Isabella
10 + 0.9*1*15 = 23.5 = 47/2 $
Hence per gallon discount is 47/50 $ = 0.94

Per gallon discount for kim = 0.5
Per gallon discount for Isabella= 0.6

0.5/0.6*100 = 120%
P.S you forgot to mention choices
Last edited by eaakbari on Sun Apr 04, 2010 11:51 pm, edited 1 time in total.
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by liferocks » Sun Apr 04, 2010 10:28 pm
I am getting the answer as 120%
consider cost per gallon as $100

Kim spend= 100*10 + 90*10 =1900-->cost per gallon 1900/20=$95
Isabella spend= 100*10 + 90*15 =2350-->cost per gallon 2350/25=$94

Discount for Kim $5/gallon
Discount for Isabella $6/gallon

hence Isabella's total per-gallon discount is 120% (6/5*100) of Kim's total per-gallon discount.
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by srinivasarajui » Sun Apr 04, 2010 10:58 pm
I agree with liferocks answer.

mitaliisrani: can you please specify the answer.
Srinu
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by pops » Sun Apr 04, 2010 11:01 pm
mitaliisrani wrote:During a special promotion, a certain filling station is offering a 10% 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?



OA: D


Please help cant figure out how to go about the sum
Discount that Kim got=10%*10
per gallon discount=10%*10/20

Discount that Isabella got=10%*15
per gallon discount=10%*15/25

Ans=10%*15/25 / 10%*10/20=120% !
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by eaakbari » Sun Apr 04, 2010 11:52 pm
Yes I made a mistake, the answer should be 120%. I have edited it now
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by harshavardhanc » Mon Apr 05, 2010 12:17 am
mitaliisrani wrote:During a special promotion, a certain filling station is offering a 10% 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?



OA: D


Please help cant figure out how to go about the sum
you just have to see on what quantity each will get discount. You need not bother about the actual discount %, since it will get canceled when you divide.

(15/25) / (10/20) * 100 = 120 %.
Regards,
Harsha
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by eaakbari » Mon Apr 05, 2010 12:33 am
harshavardhanc wrote:
mitaliisrani wrote:During a special promotion, a certain filling station is offering a 10% 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?



OA: D


Please help cant figure out how to go about the sum
you just have to see on what quantity each will get discount. You need not bother about the actual discount %, since it will get canceled when you divide.

(15/25) / (10/20) * 100 = 120 %.
Wow this is good, but could you elaborate as to how you came to this conclusion. I would have never thought of it. You rock Harsha
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by harshavardhanc » Mon Apr 05, 2010 12:51 am
eaakbari wrote:
harshavardhanc wrote:
mitaliisrani wrote:During a special promotion, a certain filling station is offering a 10% 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?



OA: D


Please help cant figure out how to go about the sum
you just have to see on what quantity each will get discount. You need not bother about the actual discount %, since it will get canceled when you divide.

(15/25) / (10/20) * 100 = 120 %.
Wow this is good, but could you elaborate as to how you came to this conclusion. I would have never thought of it. You rock Harsha
okies.

Suppose Isa purchases T gallons and gets 10% discount on X. The discount amount/gallon will be : 10% * X / T.

Suppose kim purchases t gallons and gets 10% discount on Y. The discount amount/gallon will be : 10% * Y / t.


Hence, Isa's discount : Kim's discount is (10% * X / T) : (10% * Y / t) = (X/Y) * (t/T)

So that 10% doesn't matter. it will get canceled in the calculation.
Regards,
Harsha
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