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## Homework Statement

Here is a math problem I would to make sure I have understood correctly.

a)

Billy goes to be bank. He deposite 500 dollars in his account. The bank offers a interest of 2 percent a year.

Sally goes to the bank 4 years later.She deposite 250 dollars at the same bank. But get an interest of 2.5 % a year.

write a exponential models for how much money Sally and Billy has in the bank.

b) How many years will pass before Sally has more money in her account than Billy?

## Homework Equations

[/B]

fv = pv(1+i)^n

where fv is future value, pv is the present value and i is interest and n number of years.

## The Attempt at a Solution

a) Billy: u(n) = 500 * (1.02)^n , Where n is the number of years Billy keeps his money in his account.

Sally: u(n) = 250*(1.025)^(n+4), Where n is the number of years Sally keeps his money in his account.

b) How many years will pass before Sally has more money in her account than Billy?

Calculating this isn't equal to solving:

500 * (1.02)^n = 250*(1.025)^(n+4) ??

if I solve this equation using Maple I get the result n = 121.55

But can that be right?

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