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# A certain research group plans to create computer models of

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Intern
Joined: 05 Aug 2012
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GMAT Date: 09-16-2013
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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. (x-5)/100
[Reveal] Spoiler: OA

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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) (x-5)/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) (x-5)/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:
$$(1 - \frac{x-5}{100})$$ $$=$$ $$(\frac{105-x}{100})$$

Multiplying the selection by the reduced percentage:
$$100x$$ $$(\frac{105-x}{100})$$ $$=$$ $$x(105-x)$$

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(x-5)% 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 (10-5)% = 5%

5% of 1,000 = 50

1,000 - 50 = 950

Plug x=10 into the answers and find 950.

[Reveal] Spoiler:
B

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
1
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[Reveal] Spoiler:
B

Non algebra approach:

X = 50

Before budget cost the sample contains $$10000 * .50 = 5000$$ bacteria

Budget cut will reduce sample by $$(50-5)% = 45%$$

$$45% of 5000 = 2250$$

$$5000-2250 = 2750$$

-----------------------------------
After plugging in 50 into the answer choices only
[Reveal] Spoiler:
B
yields 2750.
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Re: A certain research group plans to create computer models of [#permalink]

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11 Oct 2013, 02:37
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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) (x-5)/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 $$100x*(1-\frac{x-5}{100})=x(105-x)$$.

Hope it's clear.
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Re: A certain research group plans to create computer models of [#permalink]

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10 Jan 2014, 07:14
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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) (x-5)/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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Expert's post
WoundedTiger 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. $$\frac{x-5}{100}$$
B. x^2 – 5x
C. (x)(105 – x)
D. (100)(105 – x)
E. (100)(95 – x)

Merging topics.

Please refer to the discussion above.
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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) (x-5)/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 $$100x*(1-\frac{x-5}{100})=x(105-x)$$.

Hope it's clear.

Hi
why you wrote 1- (x-5)% in the last step? could not understand the step.

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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) (x-5)/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 $$100x*(1-\frac{x-5}{100})=x(105-x)$$.

Hope it's clear.

Hi
why you wrote 1- (x-5)% in the last step? could not understand the step.

Actually its a reduction of (x-5)%; so written in that way

x% = 100x

$$(x-5)% of 100x = 100x * \frac{(x-5)}{100}$$

$$Reduction = 100x - 100x * \frac{(x-5)}{100}$$

$$= 100x * (1 - \frac{x-5}{100})$$

= x (105-x)
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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 = 5-5=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. (x-5)/100 = 0; No

B

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-(x-5)/100 and not simply just x-5/100. 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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Bunuel can you plz explain why is it 1-(x-5)/100 and not simply just x-5/100. Thanks

Let me ask you: if x reduced by 10%, what we get 0.1x or x - 0.1x = 0.9x ?
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Re: A certain research group plans to create computer models of [#permalink]

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28 Sep 2014, 23:54
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A certain research group plans to create computer models of [#permalink]

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19 Mar 2015, 23:32
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Bunuel wrote:
Bunuel can you plz explain why is it 1-(x-5)/100 and not simply just x-5/100. 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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20 Mar 2015, 05:28
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buddyisraelgmat wrote:
Bunuel wrote:
Bunuel can you plz explain why is it 1-(x-5)/100 and not simply just x-5/100. 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

Yes, that's correct.
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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. (x-5)/100

$$10000 X% (100 - (X-5) )%$$
$$X(105 - X )$$
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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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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. (x-5)/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 (x-5)%

100x * [(1 - (x-5/100)] = 100x - x^2 +5x = 105x - x^2 -> factor out an x -> x(105-x)

Re: A certain research group plans to create computer models of   [#permalink] 21 Nov 2016, 09:33

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