When Curtis was born, his parents began depositing $1000 at the end of every year into an annuity to save for his college education. If the account paid 7% compounded annually for the first 10 years and then dropped to 5% for the next eight years, how much is the account worth now that Curtis is 18 years old and ready for college? (A formula that may be necessary is the compound interest formula A= P(1+i)^n

-- I got $13,816.45 for the first 10 years, and $9,549.11 for the last 8 years. I then added them together and got $23,365.56

Is this correct?! Any help would be appreciated :)

No, you cannot just add two sums of money if they are not in the same time slot, unless you totally ignore the compound interest.

amount
= 1000( 1.07^10 - 1)/.07 * (1.05)^8 + 1000( 1.05^8 - 1)/.05
= $29,962.30

You must be able to analyse my equation and it should make sense to you