SOLUTION: A business invests $8,000 in a savings account for two years. At the beginning of the second year an additional $2,500 is invested. At the end of the second year, the account balan

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Question 180563: A business invests $8,000 in a savings account for two years. At the beginning of the second year an additional $2,500 is invested. At the end of the second year, the account balance is $11,445. What was the annual interest rate?
Answer by Mathtut(3670) (Show Source):
You can put this solution on YOUR website!
assuming the interest rate is the same for both amounts invested
:

:

:

:
x=.05 and -2.36
:
throw out the negative
:
interest rate is %
:

Solved by pluggable solver: SOLVE quadratic equation (work shown, graph etc)

Quadratic equation (in our case ) has the following solutons:

For these solutions to exist, the discriminant should not be a negative number.

First, we need to compute the discriminant : .

Discriminant d=372490000 is greater than zero. That means that there are two solutions: .

Quadratic expression can be factored:

Again, the answer is: 0.05, -2.3625. Here's your graph: