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Of the birds in a particular aviary, 30 are both spotted and

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Of the birds in a particular aviary, 30 are both spotted and [#permalink]

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New post 10 Dec 2013, 18:48
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Of the birds in a particular aviary, 30 are both spotted and crested and 10 are neither spotted nor crested. What is the total number of birds in the aviary?

(1) The number of birds that are spotted but not crested is 10 greater than the number of birds that are crested but not spotted.

(2) More than 3/5 of the birds in the aviary are spotted.
[Reveal] Spoiler: OA

Last edited by xhimi on 11 Dec 2013, 02:47, edited 1 time in total.

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Re: Of the birds in a particular aviary, 30 are both spotted and [#permalink]

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New post 10 Dec 2013, 23:03
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xhimi wrote:
Of the birds in a particular aviary, 30 are both spotted and crested and 10 are neither spotted nor crested. What is the total number of birds in the aviary?

(1) The number of birds that are spotted but not crested is 10 greater than the number of birds that are crested but not spotted.

(2) More than 3/5 of the birds in the aviary are spotted.


Draw the venn diagram. You know this from the question stem:

Attachment:
Ques3.jpg
Ques3.jpg [ 15.47 KiB | Viewed 5981 times ]


We need to find the following Total Sum: 10 + pink region + 30 + yellow region

(1) The number of birds that are spotted but not crested is 10 greater than the number of birds that are crested but not spotted.
This says that the pink region is 10 more than the yellow region. But we have no numerical value for the pink and yellow regions.

(2) More than 3/5 of the birds in the aviary are spotted.
This says (pink region + 30) > (3/5) Total Sum
Again, we have no values for pink and yellow regions. This inequality will hold for many values of pink region and yellow region.

Taking both together, say yellow region = x, pink region = 10+x
(10 + x + 30) > (3/5)*(10 + 10 + x + 30 + x)
x < 50

Still x can take many values. For example: x = 40
Spotted birds = 70
Total birds = 110
7/11 > 3/5

x = 30
Spotted birds = 60
Total birds = 90
60/90 > 3/5

Total number of birds will be different in each case.

Answer (E)
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Re: Of the birds in a particular aviary, 30 are both spotted and [#permalink]

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Re: Of the birds in a particular aviary, 30 are both spotted and [#permalink]

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New post 08 Oct 2017, 10:47
Of the birds in a particular aviary, 30 are both spotted and crested and 10 are neither spotted nor crested. What is the total number of birds in the aviary?

(1) The number of birds that are spotted but not crested is 10 greater than the number of birds that are crested but not spotted.

(2) More than 3/5 of the birds in the aviary are spotted.

At the very least, you can use POE to elim some A/C to give yourself a fighting chance if you're low on time/not fond of these types of problems.

Q: WHAT IS THE TOTAL (ABSOLUTE) # OF BIRDS?

1) gives us a RELATIONSHIP, not an ABSOLUTE #.
> ELIM AD

2) same as "1"
> ELIM B

Now, you're duking it out between C & E. All within a matter of what, like 30 seconds?

3) when you combine the two, understand that since you're given a range of #s, you can get multiple answers...hence, C is out.
> Ans: E

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Re: Of the birds in a particular aviary, 30 are both spotted and   [#permalink] 08 Oct 2017, 10:47
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