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Re: As x increases from 209 to 210, which of the following must [#permalink]
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When x increases from 209 to 210.

I. 3x-4 will also increase as x is increasing.
II.((x-1)/x) can be written as 1-1/x.
As x increases, 1/x will decrease. That means, lesser value will be subtracted from 1 now. Hence, Increases.
III. As x increases, x^2 increase faster than x. Hence, x-x^2 will decrease.

So, Answer should be C.
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Re: As x increases from 209 to 210, which of the following must [#permalink]
What's the best way to compare such large fractions?

Bunuel wrote:
enigma123 wrote:
As x increases from 209 to 210, which of the following must increase?



II. \(\frac{x - 1}{x}\) --> \(\frac{209-1}{209}=\frac{208}{209}\) which is less than \(\frac{210-1}{210}=\frac{209}{210}\), (the same way as 1/2 is less than 2/3). Correct.

Answer: C.
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Re: As x increases from 209 to 210, which of the following must [#permalink]
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I. The answer clearly will increase as a negative constant stays the same (-4) whereas the variable with a positive constant(3x) increases.

II.
Any proper and improper fraction that gets a number added to both the numerator and the denominator gets closer to 1.
100/101 is closer to 1 than 99/100.
100/99 is further away from 1 than 101/100.
As the fraction (x-1)/x is less than 1 it will increase. (note how the question would change if II. stated (x+1)/x In that case the fraction would decrease(towards 1).

III.
The positive part (x) gets +1 whereas the negative part -(x^2) receives an exponential increase larger than 1.

I and II must increase. Answer choice: C.
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Re: As x increases from 209 to 210, which of the following must [#permalink]
ameyaprabhu wrote:
What's the best way to compare such large fractions?

Bunuel wrote:
enigma123 wrote:
As x increases from 209 to 210, which of the following must increase?



II. \(\frac{x - 1}{x}\) --> \(\frac{209-1}{209}=\frac{208}{209}\) which is less than \(\frac{210-1}{210}=\frac{209}{210}\), (the same way as 1/2 is less than 2/3). Correct.

Answer: C.


One way could be we replace the large number with a smaller one
say X will increase from 3 to 4.
let us first check the extremes.

1- 3x-4=9-4=5 and 12-4=8
8>5-Increase
2. x-1/x=(3-1)/3=2/3=2/3 and (4-1)/4=3/4
2/3>3/4 or 0.6>0.7
3. x-\(x^2\)=3-9=(-6) and 4-16=(-12)
(-6)>(-12)-decrease
hence C
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Re: As x increases from 209 to 210, which of the following must [#permalink]
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enigma123 wrote:
As x increases from 209 to 210, which of the following must increase?

I. \(3x - 4\)
II. \(\frac{x - 1}{x}\)
III. \(x - x^2\)

(A) I only
(B) III only
(C) I and II
(D) I and III
(E) II and III


We are being tested on the result when an integer is increased. So, rather than using 209 to 210, let’s use 2 to 3 (since the relationship won’t change).

I.

3(2) - 4 = 2

3(3) - 4 = 5

We see that an increase occurs.

II.

(2 - 1)/2 = 1/2

(3 - 1)/3 = 2/3

We see that an increase occurs.

III.

2 - 2^2 = -2

3 - 3^2 = -6

We see that an increase DOES NOT occur.

Answer: C
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Re: As x increases from 209 to 210, which of the following must [#permalink]
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Re: As x increases from 209 to 210, which of the following must [#permalink]
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