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

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

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New post 07 Feb 2014, 03:56
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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.

Answer: C.
[Reveal] Spoiler: OA

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

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New post 11 Aug 2014, 01:44
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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.

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

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New post 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

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

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

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New post 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.

Answer: C.


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

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

Thus
"C"

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