Question

A sum of money is invested at 4% simple interest. $500 less than three times
that amount is invested at 6% simple interest. If the total interest earned in one
year from the two investments is $1686, how much was invested at 6%

Answer 1

Let the sum invested at 4% = A
Then the sum invested at 6% = 3A - 500............(1)
1686 = 0.04A + 0.06(3A - 500)..........................(2)

Solve equation (2) to find the value of A. Then substitute the value of A in equation (1) to find the answer.