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# In a certain economy, C represents the total amount of

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Manager
Joined: 01 Sep 2012
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In a certain economy, C represents the total amount of [#permalink]  14 Dec 2012, 12:27
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60% (02:59) correct 40% (01:48) wrong based on 43 sessions
In a certain economy, C represents the total amount of consumption in millions of dollars, Y represents the total national income in millions of dollars, and the relationship between these two values is given by the equation C=90+9Y/11. If the total amount of consumption in the economy increases by 99 million dollars, what is the increase in the total national income, in millions of dollars?

A.11
B.22
C.99
D.121
E.171

I tried several different approaches any tried to input numbers to see how it reacts but nothing worked...
can someone care to explain?
[Reveal] Spoiler: OA

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Re: In a certain economy, C represents the total amount of [#permalink]  14 Dec 2012, 20:00
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roygush wrote:
In a certain economy, C represents the total amount of consumption in millions of dollars, Y represents the total national income in millions of dollars, and the relationship between these two values is given by the equation C=90+9Y/11. If the total amount of consumption in the economy increases by 99 million dollars, what is the increase in the total national income, in millions of dollars?

A.11
B.22
C.99
D.121
E.171

I tried several different approaches any tried to input numbers to see how it reacts but nothing worked...
can someone care to explain?

C_{old} = 90 + \frac{9Y_{old}}{11}

Y_{old} = \frac{(C_{old} - 90)*11}{9}

Y_{new} = \frac{(C_{old} + 99 - 90)*11}{9} = \frac{(C_{old} + 9)*11}{9}

Increase = Y_{new} - Y_{old} = \frac{(C_{old} + 9)*11}{9} - \frac{(C_{old} - 90)*11}{9} = \frac{99*11}{9}

= 121

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Manager
Joined: 01 Sep 2012
Posts: 124
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Kudos [?]: 19 [0], given: 19

Re: In a certain economy, C represents the total amount of [#permalink]  15 Dec 2012, 02:07
MacFauz wrote:
roygush wrote:
In a certain economy, C represents the total amount of consumption in millions of dollars, Y represents the total national income in millions of dollars, and the relationship between these two values is given by the equation C=90+9Y/11. If the total amount of consumption in the economy increases by 99 million dollars, what is the increase in the total national income, in millions of dollars?

A.11
B.22
C.99
D.121
E.171

I tried several different approaches any tried to input numbers to see how it reacts but nothing worked...
can someone care to explain?

C_{old} = 90 + \frac{9Y_{old}}{11}

Y_{old} = \frac{(C_{old} - 90)*11}{9}

Y_{new} = \frac{(C_{old} + 99 - 90)*11}{9} = \frac{(C_{old} + 9)*11}{9}

Increase = Y_{new} - Y_{old} = \frac{(C_{old} + 9)*11}{9} - \frac{(C_{old} - 90)*11}{9} = \frac{99*11}{9}

= 121

Ok so your thinking process was - i need to find an increase hence subtract Yold and Ynew.
I did isolated Y and then instead of C i put C+99 but wasnt aware that i should treat them as Old and New.
interesting...
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Re: In a certain economy, C represents the total amount of [#permalink]  15 Dec 2012, 04:54
Expert's post
roygush wrote:
In a certain economy, C represents the total amount of consumption in millions of dollars, Y represents the total national income in millions of dollars, and the relationship between these two values is given by the equation C=90+9Y/11. If the total amount of consumption in the economy increases by 99 million dollars, what is the increase in the total national income, in millions of dollars?

A.11
B.22
C.99
D.121
E.171

I tried several different approaches any tried to input numbers to see how it reacts but nothing worked...
can someone care to explain?

C=90+\frac{9Y}{11} --> Y=\frac{11C}{9}-9*11.

Y_1=\frac{11C}{9}-9*11;
Y_2=\frac{11(C+99)}{9}-9*11=\frac{11C}{9}+11*11-9*11=(\frac{11C}{9}-9*11)+121.

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Re: In a certain economy, C represents the total amount of [#permalink]  15 Dec 2012, 06:14
Expert's post
MacFauz wrote:
roygush wrote:
In a certain economy, C represents the total amount of consumption in millions of dollars, Y represents the total national income in millions of dollars, and the relationship between these two values is given by the equation C=90+9Y/11. If the total amount of consumption in the economy increases by 99 million dollars, what is the increase in the total national income, in millions of dollars?

A.11
B.22
C.99
D.121
E.171

I tried several different approaches any tried to input numbers to see how it reacts but nothing worked...
can someone care to explain?

C_{old} = 90 + \frac{9Y_{old}}{11}

Y_{old} = \frac{(C_{old} - 90)*11}{9}

Y_{new} = \frac{(C_{old} + 99 - 90)*11}{9} = \frac{(C_{old} + 9)*11}{9}

Increase = Y_{new} - Y_{old} = \frac{(C_{old} + 9)*11}{9} - \frac{(C_{old} - 90)*11}{9} = \frac{99*11}{9}

= 121

I like your approach step by step, is fine.

But also if we do :C = 90 + 9y/11 ------> adding 99 we have 11 (C - 90 +99)/9= y -------> 11C + 99/9 = Y clearly the only value that fits is 11 * 2 + 99/9 = y. That is, 121
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Re: In a certain economy, C represents the total amount of [#permalink]  16 Dec 2012, 03:18
Ans:
C = 90 + 9y/11 , adding 99 we have 11 (C - 90 +99)/9= y , (11C + 99)/9 = Y , so the increase is Y-y=121 the answer is (D).
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Kudos [?]: 164 [0], given: 274

Re: In a certain economy, C represents the total amount of [#permalink]  30 Jan 2014, 06:41
Just assume y=11 and C=99

Then C=198 and Y=132

So Y increases by 121

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Kudos [?]: 5079 [0], given: 164

Re: In a certain economy, C represents the total amount of [#permalink]  30 Jan 2014, 20:20
Expert's post
roygush wrote:
In a certain economy, C represents the total amount of consumption in millions of dollars, Y represents the total national income in millions of dollars, and the relationship between these two values is given by the equation C=90+9Y/11. If the total amount of consumption in the economy increases by 99 million dollars, what is the increase in the total national income, in millions of dollars?

A.11
B.22
C.99
D.121
E.171

I tried several different approaches any tried to input numbers to see how it reacts but nothing worked...
can someone care to explain?

Given C = 90 + \frac{9Y}{11}
Note that C changes whenever Y changes. So if C increases by 99, it's because Y increased from Y1 to Y2.

\frac{9}{11}(Y2 - Y1) = 99
Y2 - Y1 = 121
Y increased by 121 which led to an increase of 99 in C.
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Save $100 on Veritas Prep GMAT Courses And Admissions Consulting Enroll now. Pay later. Take advantage of Veritas Prep's flexible payment plan options. Veritas Prep Reviews Re: In a certain economy, C represents the total amount of [#permalink] 30 Jan 2014, 20:20 Similar topics Replies Last post Similar Topics: A certain bank has ten branches. What is the total amount of 3 18 Nov 2011, 13:00 A severe drought can actually lessen the total amount of 5 04 Dec 2009, 07:15 The total amount that a certain bank loaned in 1998 was$47 1 07 Oct 2008, 05:24
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