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Last year Luis invested x dollars for one year, half at 8

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Senior Manager
Joined: 25 Jun 2009
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Last year Luis invested x dollars for one year, half at 8 [#permalink]

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03 Aug 2009, 00:00
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Last year Luis invested x dollars for one year, half at 8 percent simple annual interest and the other half at 12 percent simple annual interest. Now he wants to reinvest the x dollars for one year in the same two types of investments, but the lower rate has decreased. If the higher rate is unchanged, what fraction of the x dollars must he reinvest at the 12 percent rate so that the total interest earned from the x dollars will be the
same for both years ?

(1) The lower rate is now 6 percent.
(2) The total amount of interest earned from the two investments last year was \$3,000.

[Reveal] Spoiler:
OA is A, I think it should be C

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CEO
Joined: 17 Nov 2007
Posts: 3583

Kudos [?]: 4719 [2], given: 360

Concentration: Entrepreneurship, Other
Schools: Chicago (Booth) - Class of 2011
GMAT 1: 750 Q50 V40
Re: I think OA is wrong.. ! need help ! [#permalink]

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03 Aug 2009, 00:11
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Expert's post
I think OA is correct.

half at 8% and half at 12% means 10% for x.
if we have 6% and 12% and still want to get 10% we need (my fast approach):
6 <--4-->10<--2-->12 or 4/(4+2)=2/3 invest at 12%.

It is a typical DS C-trap for % and means: often we don't need to know absolute value. So, if you are solving % problem and see absolute value only in options - be careful.
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Kudos [?]: 4719 [2], given: 360

Senior Manager
Joined: 25 Jun 2009
Posts: 298

Kudos [?]: 151 [0], given: 6

Re: I think OA is wrong.. ! need help ! [#permalink]

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03 Aug 2009, 00:22
walker wrote:
I think OA is correct.

half at 8% and half at 12% means 10% for x.
if we have 6% and 12% and still want to get 10% we need (my fast approach):
6 <--4-->10<--2-->12 or 4/(4+2)=2/3 invest at 12%.

It is a typical DS C-trap for % and means: often we don't need to know absolute value. So, if you are solving % problem and see absolute value only in options - be careful.

Thanks walker ... ! you made it easier and the fast approach is nice.. !

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Senior Manager
Joined: 17 Jul 2009
Posts: 285

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Concentration: Nonprofit, Strategy
GPA: 3.42
WE: Engineering (Computer Hardware)
Re: I think OA is wrong.. ! need help ! [#permalink]

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03 Aug 2009, 15:58
statement 1 is sufficient since the question asks for the fraction, not the actual amount...via statement 1, you'll get 1/6...to move over to 12% from 6%

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Manager
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Re: I think OA is wrong.. ! need help ! [#permalink]

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05 Aug 2009, 05:52
statement 1 is sufficient.
we need only the ratio, not the actual amount.

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Manager
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Schools: South Asian B-schools
Re: I think OA is wrong.. ! need help ! [#permalink]

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05 Aug 2009, 07:24
it will be easier to solve it with mixture and alligation approach...

given
calculate the total rate of interest ...u will see that it is x/10 hence resulting mixture will have 10% rate
mixture 1 (x/2 @ 8% ) ---->> ( total interest x @ 10%) <<---- mixture 2 ( x/2 @ 12%)
also ratio is given of split of total money x as 1:1

Statement (1) lower rate is 6%, hence a:b can be worked out ; which is nothing but our ans

mixture 1 (a @ 6% ) ---->> ( total interest x @ 10%) <<---- mixture 2 ( b @ 12%)

Statement (2) The total amount of interest \$ 3000 hence total amount is \$ 30,000 (10% interest rate resulted ...refer given) ...

mixture 1 (a @ z% ) ---->> ( total interest x @ 10% = \$ 3000) <<---- mixture 2 ( b @ 12%)

this only results in (12%-10%) / (10%-z%) = a/b ..... 2/(10-z) = a/b....after using ratio properties also it is insufficient to ans.....

Hence OA A

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Re: Last year Luis invested x dollars for one year, half at 8 [#permalink]

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29 Aug 2017, 05:16
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Re: Last year Luis invested x dollars for one year, half at 8   [#permalink] 29 Aug 2017, 05:16
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