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At the moment there are 54,210 tagged birds in a certain wildlife

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shrive555
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At the moment there are 54,210 tagged birds in a certain wildlife [#permalink] New post   26 Oct 2010, 22:49
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At the moment there are 54,210 tagged birds in a certain wildlife refuge. If exactly 20 percent of all birds in the refuge are tagged, what percent of the untagged birds must be tagged so that half of all birds in the refuge are tagged?

25
30
33 1/3
37 1/2
50
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D
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Re: At the moment there are 54,210 tagged birds in a certain wildlife [#permalink] New post   27 Oct 2010, 19:46
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Most percentage questions can be easily solved by assuming values, especially in case the answer is also a percentage.
If there are 100 birds, 20% are tagged so 20 are tagged.
Out of the rest 80, 30 should be tagged so that a total of 50% are tagged.
30/80 = 37.5%

(The huge number given is superfluous, just to make you waste your precious time. Read the question again to realize that it is not needed.)
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Re: At the moment there are 54,210 tagged birds in a certain wildlife [#permalink] New post   26 Oct 2010, 23:14
shrive555 wrote:
At the moment there are 54,210 tagged birds in a certain wildlife refuge. If exactly 20 percent of all birds in the refuge are tagged, what percent of the untagged birds must be tagged so that half of all birds in the refuge are tagged?

25
30
33 1/3
37 1/2
50


All birds = 54210
Currently Tagged = 54210 * 20/100 = 10842
So Untagged birds = 54210 - 10842 = 43368

Half of all birds = 27105
The number of birds to be tagged to make half of all birds tagged = 27105 - 10842 = 16263
So now the question remains - 16263 is how much percentage of untagged birds (43368)
= 16263 * 100 /43368
= 37.5 %
Answer (D)
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Re: At the moment there are 54,210 tagged birds in a certain wildlife [#permalink] New post   27 Oct 2010, 15:57
lengthy calculation ...
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Re: At the moment there are 54,210 tagged birds in a certain wildlife [#permalink] New post   27 Oct 2010, 16:21
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let x% of remaining birds will be tagged to increase the tagged percentage from 20 to 50

so x% * 80%= 30% hence x = 30 * 5/4 = 37.5
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Re: At the moment there are 54,210 tagged birds in a certain wildlife [#permalink] New post   31 Oct 2010, 05:10
Thank you! Karishma for such an easy solution & the tip :)
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Re: At the moment there are 54,210 tagged birds in a certain wildlife [#permalink] New post   09 Nov 2010, 10:30
Best answer Karishma!!!
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Re: At the moment there are 54,210 tagged birds in a certain wildlife [#permalink] New post   10 Dec 2010, 00:09
I approached this question as follows:

you have 20% birds tagged and to have 50% birds tagged you need to tag 30% more birds. The question is asking you how much is 30% of the the Currently untagged birds(i.e. 80%)?

So the question is what is (30/80)*100. ~ 40 and the closest option is D.

I totally agree with Karishma that the huge number is superflous and even i did waste my 30 sec on it.
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Re: At the moment there are 54,210 tagged birds in a certain wildlife [#permalink] New post   17 Mar 2021, 09:11
VeritasKarishma wrote:
Most percentage questions can be easily solved by assuming values, especially in case the answer is also a percentage.
If there are 100 birds, 20% are tagged so 20 are tagged.
Out of the rest 80, 30 should be tagged so that a total of 50% are tagged.
30/80 = 37.5%

(The huge number given is superfluous, just to make you waste your precious time. Read the question again to realize that it is not needed.)


Thanks, this is a clear explanation.
I noticed you often recommend the "weighted average" / alligation method.
Is it a case where we could have used it as well ?
When is it preferable to go percentage way vs alligation ?
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Re: At the moment there are 54,210 tagged birds in a certain wildlife [#permalink]
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