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A certain research group plans to create computer models of [#permalink]
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09 Sep 2013, 10:59
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A certain research group plans to create computer models of x% of a list of 10,000 bacterial species known to inhabit the human body. After a budget cut, the group finds it must reduce this selection by (x − 5)%. In terms of x, how many species of bacteria will the group be able to model? A. x*x – 5x B. (x)(105 – x) C. (100)(105 – x) D. (100)(95 – x) E. (x5)/100
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Last edited by suyash23n on 09 Sep 2013, 22:34, edited 3 times in total.



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Re: A certain research group plans to create computer models of [#permalink]
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09 Sep 2013, 13:35
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suyash23n wrote: A certain research group plans to create computer models of x% of a list of 10,000 bacterial species known to inhabit the human body. After a budget cut, the group finds it must reduce this selection by (x − 5)%. In terms of x, how many species of bacteria will the group be able to model?
a) x*x – 5x b) (x)(105 – x) c) (100)(105 – x) d) (100)(95 – x) e) (x5)/100 Initial: (x/100)*10000 = 100x (bacterial species) After reduce BY (x  5)%, the percentage of bacterial species = 1  (x  5)% = 1  (x  5)/100 = (105  x)/100 Note: Difference between "reduce to" [means: the remain] and "reduce by" [means: the remain = 1  "reduce by"] So, the number of bacterial species after reducing: 100x*(105  x)/100 = (x)*(105  x) Ans is B.



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Re: A certain research group plans to create computer models of [#permalink]
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09 Sep 2013, 17:20
suyash23n wrote: A certain research group plans to create computer models of x% of a list of 10,000 bacterial species known to inhabit the human body. After a budget cut, the group finds it must reduce this selection by (x − 5)%. In terms of x, how many species of bacteria will the group be able to model?
a) x*x – 5x b) (x)(105 – x) c) (100)(105 – x) d) (100)(95 – x) e) (x5)/100 I believe the OA may be wrong. I got: x% of 10000 is: \(\frac{x}{100}(10,000) = 100x\) The reduced percentage can be stated as follows: \((1  \frac{x5}{100})\) \(=\) \((\frac{105x}{100})\) Multiplying the selection by the reduced percentage: \(100x\) \((\frac{105x}{100})\) \(=\) \(x(105x)\) B
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Re: A certain research group plans to create computer models of [#permalink]
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09 Sep 2013, 18:38
I think OA is wrong too, but i got D.
out of 10,000 samples, 10,000(x5)% will be studied. If x was originally 50%, that means 5,000 would have been studied. now at 50%5%, 4,500 will be studied.
Plug in 50% for all the answers, and D=4,500.
I may be reading the questions wrong, though =/



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Re: A certain research group plans to create computer models of [#permalink]
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09 Sep 2013, 20:35
Let's say that x = 10 So 10% of 10,000 = 1,000 types of bacteria After the budget cuts, this 1,000 is reduced by (105)% = 5% 5% of 1,000 = 50 1,000  50 = 950 Plug x=10 into the answers and find 950. Answer t1000



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Re: A certain research group plans to create computer models of [#permalink]
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09 Sep 2013, 21:33
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Non algebra approach: X = 50 Before budget cost the sample contains \(10000 * .50 = 5000\) bacteria Budget cut will reduce sample by \((505)% = 45%\) \(45% of 5000 = 2250\) \(50002250 = 2750\)  After plugging in 50 into the answer choices only yields 2750.



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Re: A certain research group plans to create computer models of [#permalink]
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suyash23n wrote: A certain research group plans to create computer models of x% of a list of 10,000 bacterial species known to inhabit the human body. After a budget cut, the group finds it must reduce this selection by (x − 5)%. In terms of x, how many species of bacteria will the group be able to model?
a) x*x – 5x b) (x)(105 – x) c) (100)(105 – x) d) (100)(95 – x) e) (x5)/100 Use smart numbers. OK lets say x = 50 So then 50% of 10,000 = 5000 Now after budget cut = 5000*45/100 = (50)(45) Let's see answer choices, x = 50, target (50)(45) B does it Hope it helps Cheers J



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Re: A certain research group plans to create computer models of [#permalink]
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20 Jul 2014, 05:46



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Re: A certain research group plans to create computer models of [#permalink]
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22 Jul 2014, 13:13
Bunuel wrote: suyash23n wrote: A certain research group plans to create computer models of x% of a list of 10,000 bacterial species known to inhabit the human body. After a budget cut, the group finds it must reduce this selection by (x − 5)%. In terms of x, how many species of bacteria will the group be able to model?
a) x*x – 5x b) (x)(105 – x) c) (100)(105 – x) d) (100)(95 – x) e) (x5)/100 The number of species that the group plans to model = \(10,000*\frac{x}{100} = 100x\). After a budget cut, the group finds it must reduce this selection by (x − 5)%, thus the group will be able to model \(100x*(1\frac{x5}{100})=x(105x)\). Answer: B. Hope it's clear. Hi why you wrote 1 (x5)% in the last step? could not understand the step. Thanks in advance



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Re: A certain research group plans to create computer models of [#permalink]
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22 Jul 2014, 23:57
GGMAT760 wrote: Bunuel wrote: suyash23n wrote: A certain research group plans to create computer models of x% of a list of 10,000 bacterial species known to inhabit the human body. After a budget cut, the group finds it must reduce this selection by (x − 5)%. In terms of x, how many species of bacteria will the group be able to model?
a) x*x – 5x b) (x)(105 – x) c) (100)(105 – x) d) (100)(95 – x) e) (x5)/100 The number of species that the group plans to model = \(10,000*\frac{x}{100} = 100x\). After a budget cut, the group finds it must reduce this selection by (x − 5)%, thus the group will be able to model \(100x*(1\frac{x5}{100})=x(105x)\). Answer: B. Hope it's clear. Hi why you wrote 1 (x5)% in the last step? could not understand the step. Thanks in advance Actually its a reduction of (x5)%; so written in that way x% = 100x \((x5)% of 100x = 100x * \frac{(x5)}{100}\) \(Reduction = 100x  100x * \frac{(x5)}{100}\) \(= 100x * (1  \frac{x5}{100})\)= x (105x)
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A certain research group plans to create computer models of [#permalink]
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10 Aug 2014, 19:22
Based on the answer choices and the question, this question begs the use of x=5 as a sample number. Initial = 5%*10000 = 500 Reduction = 55=0%, so no math required here to calculate the reduction; just make sure that you can calculate 500 in your answer.
A. x*x – 5x = 0; No B. (x)(105 – x) = 500; Winner! C. (100)(105 – x) > 500; No D. (100)(95 – x) > 500; No E. (x5)/100 = 0; No
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I was a strong believer in using algebra for percent problems, but after missing 95% of them because of some careless error, I was converted to the sample number method. Generally speaking, picking smart numbers for percent problems will get you the correct answer more quickly and with the least errors.



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Re: A certain research group plans to create computer models of [#permalink]
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28 Sep 2014, 06:53
Bunuel can you plz explain why is it 1(x5)/100 and not simply just x5/100. Thanks



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Re: A certain research group plans to create computer models of [#permalink]
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28 Sep 2014, 08:56



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28 Sep 2014, 23:54
Thanks, got your point



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A certain research group plans to create computer models of [#permalink]
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Bunuel wrote: sunaimshadmani wrote: Bunuel can you plz explain why is it 1(x5)/100 and not simply just x5/100. Thanks Let me ask you: if x reduced by 10%, what we get 0.1x or x  0.1x = 0.9x ? Just to get some TRICKY basics clear 1) If 500 is reduced TO 10% ; we get 50 2) If 500 is reduced BY 10% ; we get 500  10% of 500 = 450 3) Similarly, x% less / more than y = y  / + x% of y Correct? Thanks



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Re: A certain research group plans to create computer models of [#permalink]
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Re: A certain research group plans to create computer models of [#permalink]
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20 Mar 2015, 23:19
suyash23n wrote: A certain research group plans to create computer models of x% of a list of 10,000 bacterial species known to inhabit the human body. After a budget cut, the group finds it must reduce this selection by (x − 5)%. In terms of x, how many species of bacteria will the group be able to model?
A. x*x – 5x B. (x)(105 – x) C. (100)(105 – x) D. (100)(95 – x) E. (x5)/100 \(10000 X% (100  (X5) )%\) \(X(105  X )\)
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Re: A certain research group plans to create computer models of [#permalink]
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21 Nov 2016, 09:33
suyash23n wrote: A certain research group plans to create computer models of x% of a list of 10,000 bacterial species known to inhabit the human body. After a budget cut, the group finds it must reduce this selection by (x − 5)%. In terms of x, how many species of bacteria will the group be able to model?
A. x*x – 5x B. (x)(105 – x) C. (100)(105 – x) D. (100)(95 – x) E. (x5)/100 oh...I see where I made the mistake... i chose A...what a trap... first chose: x/100 * 10,000 = 100x out of these, they need to reduce by (x5)% 100x * [(1  (x5/100)] = 100x  x^2 +5x = 105x  x^2 > factor out an x > x(105x) B is the answer.




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