We know two key circumstances: the ratio of the rates is= 3 and the earned interests are the same. It means that the 3% amount is three times as big as the 9% account. So, let the accounts are x and 3x, respectively. Then x + 3x = 10000 dollars, hence, x is $2500. ANSWER. $2500 invested at 9% and the rest, $7500, is invested at 3%.