You can put this solution on YOUR website!
Simple interest formula is Interest = (Deposit Amt. (P)) * (Interest Rate (i))
(I use P as the Deposit Amount as this is often call the Principal Amount)
The problems tells us Clara earned $360 in interest.
The problem also tells us if the interest were 3% more (i.e. i+0.03), she would have earned the same amount (360) if she deposited 1,000 less (i.e. (P-1000)).
Thus, we have the following two formulas:
Solve Eq.1 for P:
Plug the Eq.3 result into Eq. 2:
Multiply both sides by i:
Solving using the quadratic formula gives two solutions: i=.09, -.12.
|Solved by pluggable solver: SOLVE quadratic equation with variable|
|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=44100 is greater than zero. That means that there are two solutions: .
Quadratic expression can be factored:
Again, the answer is: 0.09, -0.12.
Here's your graph:
So, Clara's interest rate (i) was 9%.
Plug that into Eq.1 to get her total deposit: 360=p(.09)