# Algebra

If I have 10000 dollars and the interest rate is .40% when will my money double if compounded anually?

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1. The formula for compound interest is:

A = P * e^(r*t)

Where A = Amount, P = Principal Amount, r = Interest rate, t = Years to compound

So in your case you want to know when you will have \$20,000 so this is what you do:

\$20,000 = \$10,000 * e^(r*t)

Divide by \$10,000 on both sides:

2 = e^(.0040,t)

Take the natural logarithm of each side:

ln(2) = ln(e^(.0040*t))

ln(2) = .0040*t

Divide by .0040

ln(2)/.0040 = t

Solve using calculator:

t = 173 years

It will take approximately 173 years to turn \$10,000 to \$20,000 with a 0.40% interest rate.

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