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Lake A has a duck population of 30 females and 36 males. [#permalink]
25 May 2013, 14:27

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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?

Re: Lake A has a duck population of 30 females and 36 males. [#permalink]
25 May 2013, 14:34

7

This post received KUDOS

Expert's post

yogirb8801 wrote:

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.

Re: Lake A has a duck population of 30 females and 36 males. [#permalink]
25 May 2013, 14:46

1

This post received KUDOS

Expert's post

yogirb8801 wrote:

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?

Re: Lake A has a duck population of 30 females and 36 males. [#permalink]
31 May 2013, 12:40

I wrote a table down as following and checked which values could be plugged in

F. M. F+m+6 15 18 38 30 36 71 45 54 105 <--- stopped here 60 72 _________________

You've been walking the ocean's edge, holding up your robes to keep them dry. You must dive naked under, and deeper under, a thousand times deeper! - Rumi

Re: Lake A has a duck population of 30 females and 36 males. [#permalink]
17 Aug 2013, 19:20

manavkhurana wrote:

Why not a multiple of 17? 5 F to 6 M. If you add 6 F then 11 F to 6 M for a total of 17 ducks. So Lake B must have a multiple of 17 ducks?

How can it be a multiple of 11 if you add only female ducks? Once you add 6 female ducks, the ratio of F and M ducks changes!

Hi,

The female to male population is in the ratio 5:6. So the total duck population is 11x . It could be 11, 22 ,33 and so on. Now 6 female ducks are added to this population . In other words you are adding 6 to a multiple of 11. So the new duck population should be multiple of 11 + 6.

So the only choice that satisfies this requirement is 105 which is 99+6.

It is not a multiple of 17 because we do not have 11 female ducks for every 6 male ducks. _________________

Re: Lake A has a duck population of 30 females and 36 males. [#permalink]
17 Aug 2013, 19:37

Got it, thanks a lot!

Basically, as you stated, we are just adding 6 ducks to the original amount of ducks in lake B. If it was a multiple of 17, there would be a lot more than 6 ducks added. We do not have 11 F per 5 M, we just have 6 more ducks overall.

Re: Lake A has a duck population of 30 females and 36 males. [#permalink]
18 Aug 2013, 18:36

Bunuel wrote:

yogirb8801 wrote:

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,

I am not able to understand the question properly.

Q says the Lake population is 30 females and 36 males. and for Lake B population the Ratio of male to female is is same. i.e. 3:3.

its nowhere mentioned as Lake B population is of same ratio as Lake A.

Re: Lake A has a duck population of 30 females and 36 males. [#permalink]
19 Aug 2013, 00:46

Expert's post

rrsnathan wrote:

Bunuel wrote:

yogirb8801 wrote:

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,

I am not able to understand the question properly.

Q says the Lake population is 30 females and 36 males. and for Lake B population the Ratio of male to female is is same. i.e. 3:3.

its nowhere mentioned as Lake B population is of same ratio as Lake A.

please clarify mine plz.

Regards, Rrsnathan.

Please read the questions carefully:

Lake A has a duck population of 30 females and 36 males --> the ratio is F:M = 30:36 = 5:6. Lake B’s duck population consists of the same ratio of females to males --> F:M = 5:6. _________________

Re: Lake A has a duck population of 30 females and 36 males. [#permalink]
26 Sep 2014, 13:19

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Re: Lake A has a duck population of 30 females and 36 males. [#permalink]
28 Sep 2014, 23:56

yogirb8801 wrote:

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

As mentioned in earlier posts, we have to find answer by subtracting 6 from all 5 options & check if the resultant is divisible by 11?

What I did is, instead of subtracting 6, added 5 to all the 5 options

(Addition goes more easy with me; only result remains the same)

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