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The correct calculation is since this is Penny Kenneth wrote back
Kenneth, The factors 2% and 5% are the interest rates of the two accounts. These values are fixed, you can't change them. The 4%, which you might call the effective interest rate, is determined by how much you have in the 5% account and how much you have in the 2% account. If all your money is in the 5% account then the effective rate is 5% and if all your money is in the 2% account then the effective rate is 2%. If you have half your money in each account then the effective rate will be half way between 2% and 5%, that is (2% + 5%)/2 = 3.5%. Since your effective rate is 4%, closer to 5% than to 2%, you must have had more money in the 5% account than in the 2% account. You already determined that the weights are 2/3 and 1/3 so you must have twothirds of your money in the 5% account and onethird in the 2% account. I hope this helps,  


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