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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

1

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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

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

Only one answer choice works. Answer: C

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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