Question 255266
looks like you started off ok.


your formula is:


S = P * (1+i)^n


you used 10,000 for P and 1.21 * 10,000 = 12100 for S.


that's correct but not necessary because you could just as easily have used 1 for P and 1.21 for S.


I don't know why you filled in 4 for n.


if compounding is annually, then n should have been 2 to represent 2 years.


using your numbers for S and P, your formula should have become:


12100 = 10000 * (1+x)^2


x is the annual interest rate.


divide both sides of this equation by 10000 to get:


1.21 = (1+x)^2


take the square root of both sides of this equation to get:


{{{sqrt(1.21) = 1+x}}}


subtract 1 from both sidesof this equation to get:


{{{sqrt(1.21) - 1 = x}}}


solve for x to get:


x = .1


looks like you are looking for 10% a year growth compounded annually for 2 years.


to confirm, substitute in your original equation to get:


12100 = 10000 * (1+x)^2 becomes:


12100 = 10000 * (1.1)^2 


simplify to get:


12100 = 12100 confirming the answer is good.