Suppose you invest $50 a month in an annuity that earns 4% apr compounded monthly. how much money will you have in this account after 3 years?

To solve this we are going to use formula for the future value of an ordinary annuity: 
where
is the future value
is the periodic payment
is the interest rate in decimal form
is the number of times the interest is compounded per year
is the number of years

We know from our problem that the periodic payment is $50 and the number of years is 3, so  and . To convert the interest rate to decimal form, we are going to divide the rate by 100%


Since the interest is compounded monthly, it is compounded 12 times per year; therefore, .
Lets replace the values in our formula:




We can conclude that after 3 years you will have $1909.08 in your account.