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A total of 30 percent of the geese included in a certain

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A total of 30 percent of the geese included in a certain  [#permalink]

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New post Updated on: 07 Oct 2013, 01:29
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A total of 30 percent of the geese included in a certain migration study were male. If some of the geese migrated during the study and 20 percent of the migrating geese were male, what was the ratio of the migration rate for the male geese to the migration rate for the female geese? [Migration rate for geese of a certain sex = (number of geese of that sex migrating) / (total number of geese of that sex)]

A. 1/4
B. 7/12
C. 2/3
D. 7/8
E. 8/7

Originally posted by ajit257 on 05 Jan 2011, 18:45.
Last edited by Bunuel on 07 Oct 2013, 01:29, edited 1 time in total.
Edited the OA.
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Re: A total of 30 percent of the geese included in a certain  [#permalink]

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New post 27 Mar 2017, 17:28
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ajit257 wrote:
A total of 30 percent of the geese included in a certain migration study were male. If some of the geese migrated during the study and 20 percent of the migrating geese were male, what was the ratio of the migration rate for the male geese to the migration rate for the female geese? [Migration rate for geese of a certain sex = (number of geese of that sex migrating) / (total number of geese of that sex)]

A. 1/4
B. 7/12
C. 2/3
D. 7/8
E. 8/7


We can let t = the total number of geese before migration; thus, the number of male geese = 0.3t and the number of female geese = 0.7t. If we let the number of migrating geese = m, then the number of male migrating geese = 0.2m and the number of female migrating geese = 0.8m.

Thus, the migration rate for the male geese is 0.2m/0.3t = 2m/3t and the migration rate for the female geese is 0.8m/0.7t = 8m/7t.

Thus, the ratio of male migration rate to female migration rate is:

(2m/3t)/(8m/7t) = (7t x 2m)/(3t x 8m) = (14mt)/(24mt) = 14/24 = 7/12.

Answer: B
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Re: A total of 30 percent of the geese  [#permalink]

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New post 06 Jan 2011, 00:24
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ajit257 wrote:
A total of 30 percent of the geese included in a certain migration study were male. If
some of the geese migrated during the study and 20 percent of the migrating geese were
male, what was the ratio of the migration rate for the male geese to the migration rate for
the female geese?
[Migration rate for geese of a certain sex = (number of geese of that sex migrating) /
(total number of geese of that sex)]

A. 1/4
B. 7/12
C. 2/3
D. 7/8
E. 8/7


Let there be g geese, of which 0.3g are male and 0.7g are female
Lets say m geese migrated, 0.2m are male and 0.8m are female

Migration Rate Male = 0.2m / 0.3g = (2/3)*(m/g)
Migration Rate Female = 0.8m / 0.7g = (8/7)*(m/g)

Ratio of migration rates = (2/3) / (8/7) = 7/12

Answer is (b)
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Re: A total of 30 percent of the geese  [#permalink]

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New post 08 Oct 2013, 08:53
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rrsnathan wrote:
DaVagabond wrote:
Let' take the Number of geese to be 100.

Male = 30. Female = 70.

Now the second part of the Q, Let's take the Number migrated to be 20.

So we have 20 geese that migrated and out of that 20% are male i.e 20/100 *20 = 4 Geese (Males)

And now we know out of the total 20 geese , 4 are male , then 16 have to be female.

Now the ratio part , Male Geese Ratios = 4/30 = 2/15. - A

Female Geese Ratios =16/70=8/35 - B

Cross Multiply Equations A and B and you get =7/12 .

Ans B


Hi all,

i too tried the same method and its taking more than 3 Mins.

Please tell if there is any fast solution method.

Regards,
Rrsnathan


say 100 are geese.. 30% means 30 are male and 70 are female.

Now x geese migrates,
Therefore \(\frac{x}{5}\) are male (since 20% of migrating geeses are male) and hence \(\frac{4x}{5}\) are female

Therefore \(\frac{Migration rate male}{Migration rate female}\) = {(x/5)/30} / {(4x/5)/70}

Solving we get, 7/12 as answer.

Consider Kudos if the post helped. :-D
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Re: A total of 30 percent of the geese  [#permalink]

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New post 06 Jan 2011, 00:49
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Let' take the Number of geese to be 100.

Male = 30. Female = 70.

Now the second part of the Q, Let's take the Number migrated to be 20.

So we have 20 geese that migrated and out of that 20% are male i.e 20/100 *20 = 4 Geese (Males)

And now we know out of the total 20 geese , 4 are male , then 16 have to be female.

Now the ratio part , Male Geese Ratios = 4/30 = 2/15. - A

Female Geese Ratios =16/70=8/35 - B

Cross Multiply Equations A and B and you get =7/12 .

Ans B
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Re: A total of 30 percent of the geese included in a certain  [#permalink]

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New post 23 Mar 2017, 19:45
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Taking 100 as the number of geese in the study, 30 are male and 70 are female. Setting the number of geese that migrate as 5x, the number of male geese migrating is x (20%), and the number of female geese migrating is 4x (80%).

Ratio = (x/30)/(4x/70) = 70x/120x = 7/12

Kudos if you agree!

Please reply if you have a better solution.
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Re: A total of 30 percent of the geese included in a certain  [#permalink]

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New post 01 Jun 2016, 23:13
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rjivani wrote:
If we use the formula they give us

Isnt the migration rate the following:

Males = # geese migrating / total # of geese in sex = 0.2 (0.3x) / 0.3
Females = 0.8 * 0.7 / 0.7

Can someone help please explain why it is not the above?


0.2 * (0.3x) is a problem. The questions says that 20% of the geese migrating were males. It doesn't say that 20% of males migrated.

Sp if there were 100 geese in all, 30 were males. The question does NOT say that 20% of these 30 migrated.

Say, if half the total geese migrated, 50 migrated. Out of these 50, 20% were male i.e. 10 were male.

SO we need to take 20% of migrated geese, not the 20% of male population.

Does this sort out your problem?
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Re: A total of 30 percent of the geese included in a certain  [#permalink]

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New post 06 Jan 2018, 18:35
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rrsnathan wrote:
DaVagabond wrote:
Let' take the Number of geese to be 100.

Male = 30. Female = 70.

Now the second part of the Q, Let's take the Number migrated to be 20.

So we have 20 geese that migrated and out of that 20% are male i.e 20/100 *20 = 4 Geese (Males)

And now we know out of the total 20 geese , 4 are male , then 16 have to be female.

Now the ratio part , Male Geese Ratios = 4/30 = 2/15. - A

Female Geese Ratios =16/70=8/35 - B

Cross Multiply Equations A and B and you get =7/12 .

Ans B


Hi all,

i too tried the same method and its taking more than 3 Mins.

Please tell if there is any fast solution method.

Regards,
Rrsnathan


You could use the same method, but with simpler numbers.

30 males

70 females

Any 20/80 ratio for males migrating to females migrating will work. So, you could use the following.

10 males migrated

40 females migrated

male migration ratio: 10/30 = 1/3

female migration ratio: 40/70 = 4/7

(1/3)/(4/7) = 7/12

Choose B, and you are on to the next question. ;)

Enjoy the GAME!
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Re: A total of 30 percent of the geese included in a certain  [#permalink]

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New post 09 Jul 2019, 06:55
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Diwabag wrote:
Im surprised to see that this question is 700 level. I'm saying this not because I found it easy (I actually got it wrong) but more of it can be solved by just deeper comprehension and no sophisticated formula or deep math number theory necessary. I noticed that this is one of my weaknesses, the PERCENT within another PERCENT type of questions.

Hi Bunuel ,

Would you know some good practice questions that tests this PERCENT within a PERCENT type of question?

Thanks.


We don't have a specific sub-tag for such questions but you can search here: https://gmatclub.com/forum/search.php?s ... tag_id=191
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Re: A total of 30 percent of the geese  [#permalink]

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New post 05 Jan 2011, 23:05
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Let there be 100 geese.
Out of these since there were 30% male then there were 70 females,
let the number of migrating birds be X, out of the ones migrating 20% were males so .8x where females.
so, 7/8 (D)
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Re: A total of 30 percent of the geese  [#permalink]

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New post 07 Oct 2013, 05:54
DaVagabond wrote:
Let' take the Number of geese to be 100.

Male = 30. Female = 70.

Now the second part of the Q, Let's take the Number migrated to be 20.

So we have 20 geese that migrated and out of that 20% are male i.e 20/100 *20 = 4 Geese (Males)

And now we know out of the total 20 geese , 4 are male , then 16 have to be female.

Now the ratio part , Male Geese Ratios = 4/30 = 2/15. - A

Female Geese Ratios =16/70=8/35 - B

Cross Multiply Equations A and B and you get =7/12 .

Ans B


Hi all,

i too tried the same method and its taking more than 3 Mins.

Please tell if there is any fast solution method.

Regards,
Rrsnathan
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Re: A total of 30 percent of the geese included in a certain  [#permalink]

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New post 01 Jun 2016, 17:57
If we use the formula they give us

Isnt the migration rate the following:

Males = # geese migrating / total # of geese in sex = 0.2 (0.3x) / 0.3
Females = 0.8 * 0.7 / 0.7

Can someone help please explain why it is not the above?
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Re: A total of 30 percent of the geese included in a certain  [#permalink]

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New post 06 Jan 2018, 23:05
What level question is this?

Sent from my SM-N910C using GMAT Club Forum mobile app
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Re: A total of 30 percent of the geese included in a certain  [#permalink]

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Re: A total of 30 percent of the geese included in a certain  [#permalink]

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New post 08 Feb 2018, 17:27
MartyMurray wrote:
rrsnathan wrote:
DaVagabond wrote:
Let' take the Number of geese to be 100.

Male = 30. Female = 70.

Now the second part of the Q, Let's take the Number migrated to be 20.

So we have 20 geese that migrated and out of that 20% are male i.e 20/100 *20 = 4 Geese (Males)

And now we know out of the total 20 geese , 4 are male , then 16 have to be female.

Now the ratio part , Male Geese Ratios = 4/30 = 2/15. - A

Female Geese Ratios =16/70=8/35 - B

Cross Multiply Equations A and B and you get =7/12 .

Ans B


Hi all,

i too tried the same method and its taking more than 3 Mins.

Please tell if there is any fast solution method.

Regards,
Rrsnathan


You could use the same method, but with simpler numbers.

30 males

70 females

Any 20/80 ratio for males migrating to females migrating will work. So, you could use the following.

10 males migrated

40 females migrated

male migration ratio: 10/30 = 1/3

female migration ratio: 40/70 = 4/7

(1/3)/(4/7) = 7/12

Choose B, and you are on to the next question. ;)

Enjoy the GAME!


Great explanation! Can someone quickly point out why you divide (1/3) by (4/7) in order to take the ratio of those?

Thanks
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Re: A total of 30 percent of the geese included in a certain  [#permalink]

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New post 08 Feb 2018, 20:08
hjli89 wrote:
MartyMurray wrote:
Let' take the Number of geese to be 100.


You could use the same method, but with simpler numbers.

30 males

70 females

Any 20/80 ratio for males migrating to females migrating will work. So, you could use the following.

10 males migrated

40 females migrated

male migration ratio: 10/30 = 1/3

female migration ratio: 40/70 = 4/7

(1/3)/(4/7) = 7/12

Choose B, and you are on to the next question. ;)

Enjoy the GAME!


Great explanation! Can someone quickly point out why you divide (1/3) by (4/7) in order to take the ratio of those?

Thanks
[/quote]
[Migration rate for geese of a certain sex = (number of geese of that sex migrating) / (total number of geese of that sex)]
the migration rate for the male geese = 1/3
the migration rate for the female geese=4/7
BUT we have to find RATIO of these rates:-
"theratio of the migration rate for the male geese to the migration rate for the female geese?"

That is why we divide 1/3 by 4/7

Hope it helps
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Re: A total of 30 percent of the geese included in a certain  [#permalink]

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New post 09 Oct 2018, 23:12
Let's say 30 male and 70 female studied. Let' say, of 100 geese, 60 were migrating. 12 males migrating, 48 female migrating.
Male rate: 12/30=2/5
Female rate: 48/70=24/35
Male/Female=5*24/2*35= 7/12
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Re: A total of 30 percent of the geese included in a certain  [#permalink]

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New post 22 Mar 2019, 18:14
saw this in EP1..adding tag
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Re: A total of 30 percent of the geese included in a certain  [#permalink]

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New post 05 May 2019, 03:55
ajit257 wrote:
A total of 30 percent of the geese included in a certain migration study were male. If some of the geese migrated during the study and 20 percent of the migrating geese were male, what was the ratio of the migration rate for the male geese to the migration rate for the female geese? [Migration rate for geese of a certain sex = (number of geese of that sex migrating) / (total number of geese of that sex)]

A. 1/4
B. 7/12
C. 2/3
D. 7/8
E. 8/7


This can be solved easily using a Double Matrix Method. Refer the attached pic.
Attachments

DMatrix.PNG
DMatrix.PNG [ 40.2 KiB | Viewed 10209 times ]


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Re: A total of 30 percent of the geese included in a certain  [#permalink]

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New post 09 Jul 2019, 06:42
Im surprised to see that this question is 700 level. I'm saying this not because I found it easy (I actually got it wrong) but more of it can be solved by just deeper comprehension and no sophisticated formula or deep math number theory necessary. I noticed that this is one of my weaknesses, the PERCENT within another PERCENT type of questions.

Hi Bunuel ,

Would you know some good practice questions that tests this PERCENT within a PERCENT type of question?

Thanks.
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Re: A total of 30 percent of the geese included in a certain   [#permalink] 09 Jul 2019, 06:42
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