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Buck deposits $800 into a bank account that earns 12% interestcompounded annually.a) What is his balance after 13 years?b) How many years must pass for the account to have $13,600.05?

Sagot :

We would apply the formula for calculating compound interest which is expressed as

A = P(1 + r/n)^nt

where

A is the total amount after t years

t is the number of years

is the principal or initial amount deposited

r is the interest rate

n is the number of compounding periods in a year

From the information given,

r = 12% = 12/100 = 0.12

P = 800

n = 1 because it was compounded annually which means once per year.

a) We want to find A when t = 13. We have

A = 800(1 + 0.12/1)^1 * 13

A = 800(1 + 0.12)^13

A = 800(1.12)^13

A = 3490.79

The balance after 13 years is $3490.79

b) We want to find t when A = $13,600.05

We have

13,600.05 = 800(1 + 0.12/1)^1 *t

13,600.05 = 800(1.12/1)^t

Dividing both sides of the equation by 800, we have

13,600.05/800 = 800(1.12/1)^t/800

800 cancels out on the right. We have

17.0000625 = 1.12^t

We would take the natural log of both sides of the equation. We have

ln 17.0000625 = ln 1.12^t

On the right side, we would apply the law of logarithms which is expressed as

ln k^t = t ln k

By applying this law, we have