If you put $700 in a savings account with a 10% nominal rate of interest compounded monthly, what will the investment be worth in 21 months (round to the nearest dollar)?

To find the compound interest of an investment you have to use this formula, A = P(1 + r/n)^nt, where A is the total amount you have after the investment period, P is the amount you invest or the amount you put in, r is the rate of the of the compound interest in this case 10%, n is the amount of time the interest will be compounded for example, 4 months a year(quarterly) or 6 months a year(semi annually), and t is the amount of time you invest in years. So in this case you are going to substitute everything in the formula with their given value. So P = $700, r = 10%, n = 21 (because it is the number of months we invest for), and t = 2 years (because 21 months fit perfectly in 2 years, and t must always be in years). The resulting formula will be A = $700(1 + 0.1/21)^(21 x 2), which will give you an answer of $855 rounded to the nearest dollar.