Posted by **Cyn** on Thursday, December 3, 2009 at 7:45pm.

An amount of money is invested at 12%/a interest. Write an equation and solve it to determine the length of time it will take for the original amouunt to double if the interest is compounded annually.

- math -
**MathMate**, Thursday, December 3, 2009 at 10:33pm
The rule of 72 gives the rough period as 72/12=6 years.

The accurate calculation is as follows:

P=principal

R=interest rate= 1.12 for 12%

n=number of years required.

So

PR^{n}=2P

R^{n}=2

Take log on both sides,

log(R^{n}=log(2)

n*log(R) = log(2)

n=log(2)/log(R)

=log(2)/log(1.12)

=0.3010/0.0492

=6.116 years.

## Answer This Question

## Related Questions

- algebra - A total of $12,000 is invested in two funds paying 9% and 11% simple ...
- math - A student invests two sums of money at 3% and 4% interest, receiving a ...
- math - An investment of $3,000 is made at an annual simple interest of 5%. How ...
- Algebra - I invested $42,000 in three funds paying 5%, 7%, and 9% simple ...
- math - Money is invested at two rates of interest. One rate is 8% and the other ...
- Math - A=P(1+r)^2 A= interest P= principle interest r= interest rate t= time in ...
- math - Sam invested $5000 in a GIC earning 8% compound interest per year. The ...
- algebra - Money is invested at two rates of interest. One rate is 8% and the ...
- algebra - Dilbert invests a total of $14,000 in two accounts paying 9% and 15% ...
- math - An investor receives a total of Rs.5,700 per annum in interest from 3 ...

More Related Questions