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# For which of the following expressions would the value be

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Manager
Joined: 17 Sep 2011
Posts: 164
For which of the following expressions would the value be [#permalink]

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01 Feb 2012, 20:05
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Question Stats:

78% (01:04) correct 22% (02:01) wrong based on 139 sessions

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For which of the following expressions would the value be greater if 160 were replaced by 120 ?

A) 1000- 160

B) 160/(1+160)

C) 1/(1-1/160)

The answer choices are listed below

1) None
2) A only
3) C only
4) A & B
5) A & C

Could please provide a solution to this problem ?
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Intern
Joined: 04 Mar 2011
Posts: 18
Re: For which of the following expressions would the value be gr [#permalink]

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01 Feb 2012, 22:05
answer should be A & C

a) 1000-160 = 840 vs 1000-120 = 880 so it is higher

b) 160/161 is bigger than 120/121

c) 1/(1-1/160) vs 1/(1-1/120) you really dont need to work it out

you can compare the 1-1/160 vs the 1-1/120 the 1/120 will reduce it more than the 1/160 since its a larger number but it is at the bottom of a fraction so it will make the value bigger overall.
Intern
Joined: 31 Jan 2012
Posts: 6
Concentration: Finance, Economics
GPA: 2.98
Re: For which of the following expressions would the value be [#permalink]

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03 Mar 2012, 01:47
I am getting "A only." Because doesn't 1/(1-1/160) put 0 in the denominator which cannot happen?
Math Expert
Joined: 02 Sep 2009
Posts: 46319
Re: For which of the following expressions would the value be [#permalink]

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03 Mar 2012, 01:52
Mercury14 wrote:
I am getting "A only." Because doesn't 1/(1-1/160) put 0 in the denominator which cannot happen?

It's $$\frac{1}{1-\frac{1}{160}}$$. On the GMAT you won't see a denominator equal to zero, since the division by zero is not allowed.
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Intern
Joined: 31 Jan 2012
Posts: 6
Concentration: Finance, Economics
GPA: 2.98
Re: For which of the following expressions would the value be [#permalink]

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03 Mar 2012, 02:01
Oh ok. Thanks. I wasn't looking at it that way.
Manager
Joined: 30 May 2012
Posts: 215
Location: United States (TX)
Concentration: Finance, Marketing
GPA: 3.3
WE: Information Technology (Consulting)
Re: For which of the following expressions would the value be [#permalink]

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20 Aug 2017, 16:28
Can someone tell how to quickly identify which is bigger between fractions that are greater than 1?
For e.g, between 120/121 and 160/161, how could one tell which is bigger in about 30 secs? Bunuel, any help here, please?
Math Expert
Joined: 02 Sep 2009
Posts: 46319
Re: For which of the following expressions would the value be [#permalink]

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21 Aug 2017, 02:28
1
Blackbox wrote:
Can someone tell how to quickly identify which is bigger between fractions that are greater than 1?
For e.g, between 120/121 and 160/161, how could one tell which is bigger in about 30 secs? Bunuel, any help here, please?

We have an article on this: GMAT Shortcut: Adding to the Numerator and Denominator.

Hope it helps.
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Manager
Joined: 30 May 2012
Posts: 215
Location: United States (TX)
Concentration: Finance, Marketing
GPA: 3.3
WE: Information Technology (Consulting)
Re: For which of the following expressions would the value be [#permalink]

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21 Aug 2017, 09:16
Thanks. I shall look into the article.
Manager
Joined: 04 May 2014
Posts: 162
Location: India
WE: Sales (Mutual Funds and Brokerage)
Re: For which of the following expressions would the value be [#permalink]

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21 Aug 2017, 19:29
A) 1000- 160=840
1000-120=880>840

B) 160/(1+160)=160/161
120/(1+120)=120/121
to check which fraction is bigger cross multiply 160*121=19360 and 161*121=19320 hence 160/161>120/121

C) 1/(1-1/160)=1/(160-1)/160=1/159/160=160/159
1/(1-1/120)=1/(120=1)/120=1/119/120=120/119
cross multiply 160*119=19040
159*120=19080>19040
hence A & C.
Manager
Joined: 30 May 2012
Posts: 215
Location: United States (TX)
Concentration: Finance, Marketing
GPA: 3.3
WE: Information Technology (Consulting)
Re: For which of the following expressions would the value be [#permalink]

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21 Aug 2017, 20:30
gps5441 wrote:
A) 1000- 160=840
1000-120=880>840

B) 160/(1+160)=160/161
120/(1+120)=120/121
to check which fraction is bigger cross multiply 160*121=19360 and 161*121=19320 hence 160/161>120/121

C) 1/(1-1/160)=1/(160-1)/160=1/159/160=160/159
1/(1-1/120)=1/(120=1)/120=1/119/120=120/119
cross multiply 160*119=19040
159*120=19080>19040
hence A & C.

GPS - You're correct about cross-multiplying the Ns and Ds. But there ought to be a quicker way other than that... maybe in the article that Bunuel referred to?!
Re: For which of the following expressions would the value be   [#permalink] 21 Aug 2017, 20:30
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