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To travel trip of 40 miles?the speed for the first Y miles

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CEO
Joined: 15 Aug 2003
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To travel trip of 40 miles?the speed for the first Y miles [#permalink]  22 Sep 2003, 13:19
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1.To travel trip of 40 miles?the speed for the first Y miles was
X, and the speed for the remaining 40-y is 1.2X. what's the average
speed?
1) x=12 m/h 2) y=20

2.The 'rule of 72', defining the time needed for the investment to
double, is K/2, where K means the percentage interest to be
compounded yearly. If an investment of $10,000 is invested at the annual rate of 8%. And after the investment yields to be$20,000, and
again be invested at the annual rate of 12%. Then according to the
'rule of 72', how long will it take the original to yield a total of
\$40,000?
SVP
Joined: 03 Feb 2003
Posts: 1608
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(2) 10 years to transform 10000 into 40000.
GMAT Club Legend
Joined: 15 Dec 2003
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For Q2, the answer should be 15 years. The question is wrong. Rule of 72 should be '72/interest rate' for an investment to double. You can try it yourself on your calculator. Therefore, at 8%, it will take 72/8 = 9 years for first portion to double. Then 72/12 = 6 years to double again at 12%. Then 9+6 = 15 years.

Quote:
Q2 - is it 4+6 = 10 ?
Besides it doesn't make sense that at 8% interest, it takes only 4 years to double as opposed to 6 years when interest rates are at 12%.
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Best Regards,

Paul

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Joined: 26 Dec 2003
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Location: India
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10 yrs , 4 yrs from 10,000 to 20,000 and 6 yrs from 20,000 to 40,000
SVP
Joined: 30 Oct 2003
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Location: NewJersey USA
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This is a wierd question.
I just did k/2 to arrive at the result.
However at 1.08 interest rate it takes 9 years and at 12 % interest rate it takes approx 6 years to double the money.

I had to use log function in my calculator you know.

Praetorian should post the answer. I guess he ( I assume it is he ) has posted so many Qs and may be does not have enough time to go through his mail and see each response.

Hi paul,
You pretty much get to the page I am in a matter of couple of days. Looks like you are beating your head on Quant section now. Good luck to you anyway.
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