## Trending News

# pre calc help?

You want to make an investment in a continuously compounding account over a period of 20 years. What interest rate is required for your investment to double in that time period? Round the logarithm value to the nearest hundredth and the answer to the nearest tenth.You want to make an investment in a continuously compounding account over a period of 20 years. What interest rate is required for your investment to double in that time period? Round the logarithm value to the nearest hundredth and the answer to the nearest tenth.

The letters r and θ represent polar coordinates. Write the following equation using rectangular coordinates (x, y).

r= 5/1+cosθ

### 3 Answers

- Mike GLv 711 months agoFavorite Answer
2 = e^(20r)

ln2 = 20r

r = 0.034657

Answer r = 3.5%

[For a gross error check use the rule of 72

72/20 = 3.6%]✓

- Login to reply the answers

- SpacemanLv 711 months ago
FV = future value of investment

PV = present value of investment

e = base of natural logarithms = 2.718281828

Y = number of years of investment = 20 years

r = annual interest rate = to be determined

FV = PV*e^Yr

FV/PV = e^Yr

FV/PV = 2 (investment value doubles)

2 = e^Yr

ln(2) = ln(e^Yr)

ln(2) = Yr[ln(e)]

ln(2) = Yr(1)

ln(2) = Yr

ln(2)/Y = r

r = ln(2)/Y

r = ln(2)/20

r = 0.034657359 = 0.03 logarithm value

r = 3.5% interest rate

Source(s): http://www.moneychimp.com/articles/finworks/contin... http://www.sosmath.com/algebra/logs/log4/log46/log...- Login to reply the answers

- Jeff AaronLv 711 months ago
The formula for continuous compounding is:

A = Pe^(rt)

To double the investment, A/P = 2, i.e. e^(rt) = 2, and since t = 20, we have:

e^(20t) = 2

Since t is a real number, 20t is a real number, so we have:

20t = ln(2)

t = ln(2)/20

t =~ 0.034657359027997265470861606072909

So the interest rate should be about 3.4657%

- Login to reply the answers