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If 25 percent of a certain number is 1,600, what is 10 perce

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If 25 percent of a certain number is 1,600, what is 10 perce [#permalink]  09 May 2018, 10:06
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If 25 percent of a certain number is 1,600, what is 10 percent of the number?

(A) 40

(B) 400

(C) 640

(D) 1,440

(E) 4,000
[Reveal] Spoiler: OA

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Re: If 25 percent of a certain number is 1,600, what is 10 perce [#permalink]  09 May 2018, 13:08
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Carcass wrote:
If 25 percent of a certain number is 1,600, what is 10 percent of the number?

(A) 40
(B) 400
(C) 640
(D) 1,440
(E) 4,000

IMPORTANT: We need not actually determine the number in question.

Given: 25% of a certain number is 1600
So, we know that 50% of the number is 3200
And 500% of the number is 32000
etc.

So, let's use the same logic to approximate the correct answer:
Given: 25% of a certain number is 1600
So, 12.5% of the number is 800
And 6.25% of the number is 400

Since 25% is BETWEEN 6.25% and 12.5%, we know that the correct answer is BETWEEN 400 and 800

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Re: If 25 percent of a certain number is 1,600, what is 10 perce [#permalink]  09 May 2018, 13:10
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I know that this below method is not usually the preferred 'easy' way, but I have been doing like this for a while now and I could solve this in 30seconds:
Let number be x. i.e 25x/100=1600. x= (1600*100)/25=6400. (6400*10)/100= 640
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Re: If 25 percent of a certain number is 1,600, what is 10 perce [#permalink]  27 Jun 2018, 16:15
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Expert's post
Carcass wrote:
If 25 percent of a certain number is 1,600, what is 10 percent of the number?

(A) 40

(B) 400

(C) 640

(D) 1,440

(E) 4,000

We can let n = the number in question and create the equation:

0.25n = 1,600

n = 6,400

So 10% of 6,400 is 0.1 x 6,400 = 640.

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Re: If 25 percent of a certain number is 1,600, what is 10 perce [#permalink]  15 Jan 2019, 15:54
GreenlightTestPrep wrote:
Since 25% is BETWEEN 6.25% and 12.5%,

Is it 25% or 10%?
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Re: If 25 percent of a certain number is 1,600, what is 10 perce [#permalink]  17 Jan 2019, 05:20
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Translation: 25 percent of a certain number is 1,600

$$0.25 x = 1600$$

$$x = \frac{1600}{0.25} = 6400$$

Then

$$0.1 of 6400 = 640$$

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Re: If 25 percent of a certain number is 1,600, what is 10 perce [#permalink]  17 Jan 2019, 06:38
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AE wrote:
GreenlightTestPrep wrote:
Since 25% is BETWEEN 6.25% and 12.5%,

Is it 25% or 10%?

It is a typo.. it should be 10%
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Some useful Theory.
1. Arithmetic and Geometric progressions : https://greprepclub.com/forum/progressions-arithmetic-geometric-and-harmonic-11574.html#p27048
2. Effect of Arithmetic Operations on fraction : https://greprepclub.com/forum/effects-of-arithmetic-operations-on-fractions-11573.html?sid=d570445335a783891cd4d48a17db9825
3. Remainders : https://greprepclub.com/forum/remainders-what-you-should-know-11524.html
4. Number properties : https://greprepclub.com/forum/number-property-all-you-require-11518.html
5. Absolute Modulus and Inequalities : https://greprepclub.com/forum/absolute-modulus-a-better-understanding-11281.html

Re: If 25 percent of a certain number is 1,600, what is 10 perce   [#permalink] 17 Jan 2019, 06:38
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