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In a certain district, the ratio of the number of registered

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Manager
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Re: In a certain district, the ratio of the number of registered  [#permalink]

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New post 27 Oct 2016, 09:20
Bunuel Can you please guide where I am getting wrong ?

R/D = 3/5 -----(1)

R+600 / D+500 = 4/5 ----(2)

Solving (2) we get

1000 = 4D - 5R

Substitute value of R from (1)

1000 = 4D - 5* (3D/5)

D = 1000

Hence R = 600

So difference should be 400 ??
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Re: In a certain district, the ratio of the number of registered  [#permalink]

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New post 27 Oct 2016, 10:05
3
The difference of 400 is before the new registrations. But the problems asks for "After these (new) registrations..." So the new number of registered Republicans is 600 + 600 = 1200, and the new number of registered Democrats is 1000 + 500 = 1500. So the difference is 300.

Does that make sense?
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Re: In a certain district, the ratio of the number of registered  [#permalink]

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New post 27 Oct 2016, 10:25
ScottTargetTestPrep wrote:
The difference of 400 is before the new registrations. But the problems asks for "After these (new) registrations..." So the new number of registered Republicans is 600 + 600 = 1200, and the new number of registered Democrats is 1000 + 500 = 1500. So the difference is 300.

Does that make sense?


I agree to your explanation as its evident from the answer.

My query is algebraically where I am getting wrong? Is it that at the time if expressing a Q into ratios , we need to provide a constant 'k' or 'x' everytime
What is the significance of this constant?
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Re: In a certain district, the ratio of the number of registered  [#permalink]

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New post 31 Oct 2016, 08:46
I think you're getting confused with the variables that you created. When you make up variables in your equation, you need to know what those variables stand for - what they represent.. For example, what does the variable D correspond to? Right? Otherwise, your algebra looks fine. You just have to be careful to answer the question that is being asked. I hope this helps...
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In a certain district, the ratio of the number of registered  [#permalink]

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New post 31 Oct 2016, 19:54
Walkabout wrote:
In a certain district, the ratio of the number of registered Republicans to the number of registered Democrats was 3/5. After 600 additional Republicans and 500 additional Democrats registered, the ratio was 4/5. After these registrations, there were how many more voters in the district registered as Democrats than as Republicans?

(A) 100
(B) 300
(C) 400
(D) 1,000
(E) 2,500


let t=total original registrations
3/8*t+600=4/9*(t+1100)
t=1600
t+1100=2700 revised total
5/9*2700=1500 democrats
4/9*2700=1200 republicans
1500-1200=300
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Re: In a certain district, the ratio of the number of registered  [#permalink]

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New post 03 Nov 2017, 07:24
Does anybody know a solution with the ratio box?
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Re: In a certain district, the ratio of the number of registered  [#permalink]

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New post 28 Apr 2019, 14:20
Bunuel
Could it be solved this way?

- 500 Resp and 600 Demo joined the registration
- the number of people "behind" the ratio is stable (I mean what amount of people 1 Resp and 1 Demo in the ratio represent)
- from the final ratio 4/5 we see that the difference is just one "number behind the ratio"
- since joined 500 resp and 600 demo do not convert ratio to irrational (like 4.12/5.06) we conclude that the "number behind the ratio" is a multiple of 5 and 6
- so we have steps of 30 people to represent "the number behind the ratio" (it could be 30, 60, 90, 120, 150... 300... 600... and so on).
- do not plug these values into the ratio. Just see what number from the answer choices represent multiple of 30.
- only B fits.
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Re: In a certain district, the ratio of the number of registered   [#permalink] 28 Apr 2019, 14:20

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