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# A sum of money doubles itself at a compound interest in 15 y

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Math Expert
Joined: 02 Sep 2009
Posts: 41717

Kudos [?]: 124948 [0], given: 12079

Re: A sum of money doubles itself at a compound interest in 15 y [#permalink]

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07 Feb 2014, 03:56
Expert's post
5
This post was
BOOKMARKED
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Difficulty:

5% (low)

Question Stats:

74% (00:36) correct 26% (00:37) wrong based on 203 sessions

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aimlockfire1 wrote:
A sum of money doubles itself at a compound interest in 15 years . In how may years it will become 8 times ??

a) 30 years

b) 40 years

c) 45 years

d) 50 years

e) 60 years

If the sum doubles (x2) in 15 years, then it to become 2*2*2 = 8 times as large it should double three times, so three 15 years time period are needed, which is 3*15 = 45 years.

[Reveal] Spoiler: OA

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Kudos [?]: 124948 [0], given: 12079

Current Student
Joined: 21 Oct 2013
Posts: 193

Kudos [?]: 42 [1], given: 19

Location: Germany
GMAT 1: 660 Q45 V36
GPA: 3.51
Re: A sum of money doubles itself at a compound interest in 15 y [#permalink]

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11 Aug 2014, 01:44
1
KUDOS
Let's say amount of money = \$2, then 8 times = 16 \$

Then
Year 00 = 2 \$
Year 15 = 4 \$
Year 30 = 8 \$
Year 45 = 16 \$ --> this is our answer, hence C.

Kudos [?]: 42 [1], given: 19

SVP
Status: The Best Or Nothing
Joined: 27 Dec 2012
Posts: 1854

Kudos [?]: 2527 [0], given: 193

Location: India
Concentration: General Management, Technology
WE: Information Technology (Computer Software)
A sum of money doubles itself at a compound interest in 15 y [#permalink]

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13 Aug 2014, 02:15
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Say initial amount = 100

Final amount = 800

100 >>>>>>>> 200 >>>>>>>>> 400 >>>>>>>>>> 800

........... 15 ............ 15 ................. 15

Total = 15*3 = 45

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Kudos [?]: 2527 [0], given: 193

GMAT Club Legend
Joined: 09 Sep 2013
Posts: 17669

Kudos [?]: 272 [0], given: 0

Re: A sum of money doubles itself at a compound interest in 15 y [#permalink]

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05 Jul 2016, 12:25
Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

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Joined: 12 Nov 2016
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Kudos [?]: 32 [0], given: 158

Re: A sum of money doubles itself at a compound interest in 15 y [#permalink]

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21 Jun 2017, 05:18
Bunuel wrote:
aimlockfire1 wrote:
A sum of money doubles itself at a compound interest in 15 years . In how may years it will become 8 times ??

a) 30 years

b) 40 years

c) 45 years

d) 50 years

e) 60 years

If the sum doubles (x2) in 15 years, then it to become 2*2*2 = 8 times as large it should double three times, so three 15 years time period are needed, which is 3*15 = 45 years.

If the lump sum is 8x then this represents a 2x^3 increase to

x(1 +r)^15(3)= 8x

Thus
"C"

Kudos [?]: 32 [0], given: 158

Re: A sum of money doubles itself at a compound interest in 15 y   [#permalink] 21 Jun 2017, 05:18
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