# Math Help - interest rates.

1. ## interest rates.

I'm not sure if this belongs here or not- I am taking a contemporary mathematics course this semester and I missed a day of class. The name of the title is Finding interest rates.

I already have the anwser, just need someone's help explaining how to solve the problem.
For example: Suppose you invest $10,000 on your son's 13th birthday and it accumulates to 15,000 on his 18th birthday. What annual rate of compound interest did this investment earn? Pv=10,000 fv=15,000 t=5 years answer 8.45% Please help me. 2. The compound interest formula is $F_v = P_v \left(1 + \dfrac{r}{n}\right)^{nt}$ where • $F_v$ = Final Value • $P_v$ = Initial Value • $r$ = Annualised interest rate • $n$ = number of compounds per year • $t$ = number of years You know $F_v = 15000$, $P_v = 10000$, $n = 1$ (it's compounded annually) and $t = 5$ Plug and Chug gives: $r = \sqrt[5]{\dfrac{F_v}{P_v}} - 1$ 3. Originally Posted by candisweet I'm not sure if this belongs here or not- I am taking a contemporary mathematics course this semester and I missed a day of class. The name of the title is Finding interest rates. I already have the anwser, just need someone's help explaining how to solve the problem. For example: Suppose you invest$10,000 on your son's 13th birthday and it accumulates to 15,000 on his 18th birthday. What annual rate of compound interest did this investment earn?

Pv=10,000 fv=15,000 t=5 years answer 8.45%

Well the compound interest formula is

$\displaystyle P=P_0\left(1+\frac{r}{n}\right)^{nt}$

and you are given $P=15000,P_0=100000,n=1,t=5$
Putting all of this into the equation gives

$\displaystyle 15000=10000\left(1+r\right)^{5}$

Can you finish from here?

Edit: too slow

4. I know how to set the initial problem, but I guess what I'm asking is for the detailed steps because I cant figure it out, like how to isolate r, I think. Im so confused. Sorry math is not my thing.

I get to here.

15,000=10,000(1 + r) 5
(15,000 /10,000 -1) = r 5
don't know how to go further.

5. You have (1+r)^5 which is definitely not "r 5"

I have solved the equation for r in post 2 (but note that you take the 5th root before subtracting 1)

If your calculator does not have a 5th root button raise it to the power of 0.2

6. Thanks. I wasn't using my calculator right. I got the answer! thanks so much

7. REMEMBER: if a^p = b, then a = b^(1/p) ; TATTOO that on your wrist !