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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: 52119
A sum of money doubles itself at a compound interest in 15 y  [#permalink]

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07 Feb 2014, 02:56
00:00

Difficulty:

5% (low)

Question Stats:

78% (00:40) correct 22% (00:43) wrong based on 273 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.

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

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11 Aug 2014, 00:44
2
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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Re: A sum of money doubles itself at a compound interest in 15 y  [#permalink]

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13 Aug 2014, 01:15
3
1
Say initial amount = 100

Final amount = 800

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

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

Total = 15*3 = 45

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

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21 Jun 2017, 04:18
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"
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Re: A sum of money doubles itself at a compound interest in 15 y  [#permalink]

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09 Jan 2019, 08:35
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Re: A sum of money doubles itself at a compound interest in 15 y &nbs [#permalink] 09 Jan 2019, 08:35
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# A sum of money doubles itself at a compound interest in 15 y

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