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Re: The price of a pastry at 10AM was $p. Each hour after 11AM, the price [#permalink]
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can be done by assuming the initial price i.e. price of the pastry 10 AM - > 10

10 AM - > $10 (price paid by Julie)
11 - > $10 *.8 -> $ 8 (price paid by Julie)
12 - > $8 * .8 - > $ 6.4
1 -> $6.4 * .8 -> $ 5.12
@ 2 -> $5.12*.8 -> 4.096

price paid of Julie's sis - > 4.096

% difference= > (4.096/8) -> here numerator is greater than 50% of 8, thus the %value will be slightly lower than 50%.

from the given choices - > only C works out as an option. thus ANS - > C
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Re: The price of a pastry at 10AM was $p. Each hour after 11AM, the price [#permalink]
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akurathi12 wrote:
The price of a pastry at 10 AM was $p. Each hour after 11 AM, the price decreases by 20%. If Julie bought the pastry at 11:15 AM whereas her sister bought the same 3 hours later, then the price paid by Julie's sister was what percent less than that paid by Julie?(There is no price change apart from those mentioned above)

A. 33.33%
B. 37.5%
C. 48.8%
D. 51.2%
E. None of these


There is a reduction of 20% every hour so the price becomes (4/5) of what it was in the previous hour.

At 11:15, Julie bought the pastry for p*(4/5)
3 hrs later, at 2:15, her sister bought the pastry for p*(4/5)*(4/5)^3 = p*(4/5)^4 = p*(256/625)

% Diff = [p*(4/5) - p*(256/625)] / p*(4/5) = 1 - (256 * 5)/(625 * 4) = 61/125 = 48.8% ( because 61 is a bit less than 62.5 which is half of 125)

Answer (C)
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Re: The price of a pastry at 10AM was $p. Each hour after 11AM, the price [#permalink]
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Julie will by it at $p. Her sister will buy it at

0.8x0.8x0.8p = 0.512p.

Percentage decrease =


p-0.512p

= 0.488p

0.488p/p x 100 = 48.8%

Posted from my mobile device
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Re: The price of a pastry at 10AM was $p. Each hour after 11AM, the price [#permalink]
 
akurathi12 wrote:
The price of a pastry at 10 AM was $p. Each hour after 11 AM, the price decreases by 20%. If Julie bought the pastry at 11:15 AM whereas her sister bought the same 3 hours later, then the price paid by Julie's sister was what percent less than that paid by Julie?(There is no price change apart from those mentioned above)

A. 33.33%
B. 37.5%
C. 48.8%
D. 51.2%
E. None of these

­KarishmaB Ma'am have a very basic doubt, How to read "then the price paid by Julie's sister was what percent less than that paid by Julie?" is it same as "price paid by Julie's sister was what percent than that paid by Julie?"?  
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Re: The price of a pastry at 10AM was $p. Each hour after 11AM, the price [#permalink]
Let p$ be 100$
Julie bought the pastry at 100$
Julie's sister bought the pastry at 100$ -20% =80$
80$ - 20% = 64$
64$ - 20% = 51.2$

Julie's sister paid = 48.8% less

((51.2$-100)/100*100)= 48.8%
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