You invest $2,200 at an interest rate that is compounded annually. After 8 years, your principal has increased to $3,128.62. What percent is the interest rate?

Question

anonymous · Answer

much oblidged

anonymous · Answer

$$3128.62=2200\times (1+r)^8$$ solve for r

anonymous · Answer

i would assume that u divide 2200 first which would give u 1.4221

anonymous · Answer

$$(1+r)^8=\frac{3128.62}{2200}$$ 
$$1+r=\sqrt[8]{\frac{3128.62}{2200}}$$

anonymous · Answer

yeah divide.  then take the 8th root.  then subtract 1.  then turn answer into a percent if that is what they want

anonymous · Answer

you will need a nice calculator to take the 8th root.

anonymous · Answer

root:8:(3128.62/2200)=1.0449999437

anonymous · Answer

so the percent would b 4%, right?

anonymous · Answer

i get the 8th root at 1.044999... so 
r = .044999 =4.45% rounded

anonymous · Answer

i would keep a couple decimal places, but yes, you have it

anonymous · Answer

it was 4.5 but at least i learned something

anonymous · Answer

excuse me i mean 4.5%

anonymous · Answer

i rounded incorrectly as you see.  should round 4.4999 to 4.5