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Lake A has a duck population of 30 females and 36 males. 08 Jul 2018, 05:46
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Thanks!
Although I could solve it correctly, but your method saved a lot of time.
gultrage
the ratio is 5:6
So let the female ducks be 5x and male be 6x.
Total duck=11x
Now 11x+6 should divide one of the options.
105-6=99
Therefore ans is B
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Lake A has a duck population of 30 females and 36 males. 01 May 2021, 15:03
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Bunuel
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Lake A has a duck population of 30 females and 36 males. Lake B’s duck population consists of the same ratio of females to males. If 6 new female ducks are added to Lake B and no other ducks are added or removed, the new total duck population of Lake B could be which of the following?

A. 144
B. 105
C. 78
D. 51
E. 36

The ratio of females to males in Lake B is 30:36 = 5:6 --> the total number of ducks in Lake B must be a multiple of (5+6)=11.

When 6 new female ducks are added to Lake B, the total number of ducks in Lake B becomes a multiple of 11 plus 6.

Only 105 is a multiple of 11 plus 6: 9*11+6=105.

Answer: B.

Hope it's clear.
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Hi Bunuel

Thanks for the explanation and extra practice questions you posted. I struggle a lot with questions of this type (where something is added or subtracted from another ratio). Is there a post on the theoretical concepts that I can use to learn this? I would like to get my concepts clear before diving into difficult problems of this nature. Thanks a lot in advance!
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Lake A has a duck population of 30 females and 36 males. 01 May 2021, 15:20
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UserMaple5
Bunuel
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Lake A has a duck population of 30 females and 36 males. Lake B’s duck population consists of the same ratio of females to males. If 6 new female ducks are added to Lake B and no other ducks are added or removed, the new total duck population of Lake B could be which of the following?

A. 144
B. 105
C. 78
D. 51
E. 36

The ratio of females to males in Lake B is 30:36 = 5:6 --> the total number of ducks in Lake B must be a multiple of (5+6)=11.

When 6 new female ducks are added to Lake B, the total number of ducks in Lake B becomes a multiple of 11 plus 6.

Only 105 is a multiple of 11 plus 6: 9*11+6=105.

Answer: B.

Hope it's clear.



Hi Bunuel

Thanks for the explanation and extra practice questions you posted. I struggle a lot with questions of this type (where something is added or subtracted from another ratio). Is there a post on the theoretical concepts that I can use to learn this? I would like to get my concepts clear before diving into difficult problems of this nature. Thanks a lot in advance!
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3. Fractions, Decimals, Ratios and Proportions



For other topics check Ultimate GMAT Quantitative Megathread

Hope it helps.
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Lake A has a duck population of 30 females and 36 males. 02 May 2021, 13:20
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I'm not an English native speaker, but this question seems ill-defined to me. The expression "Lake B’s duck population consists of the same ratio of females to males" could easily be interpreted as Lake B having a ratio of 1:1.

IMO the sentence would be better defined as "Lake B’s duck population consists of the same ratio of females to males as Lake A."

Am I crazy about this?
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Lake A has a duck population of 30 females and 36 males. 02 May 2021, 13:58
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giannilorenz
I'm not an English native speaker, but this question seems ill-defined to me. The expression "Lake B’s duck population consists of the same ratio of females to males" could easily be interpreted as Lake B having a ratio of 1:1.

IMO the sentence would be better defined as "Lake B’s duck population consists of the same ratio of females to males as Lake A."

Am I crazy about this?
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I can understand the confusion and agree that the sentence could have been more clear. However in the context of this problem, we are given info about Lake A and my instinct is to look for ways to use the given info. In this case we cannot solve without using the info on Lake A
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Lake A has a duck population of 30 females and 36 males. 30 Apr 2026, 02:13
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