Equal amounts are invested at 6%, 7%, and 8% annual interest. If the three investments yeild a total of $52.50 annual interest, find the total investment.
lets say we invest x dollars in each account. so the total investment is 3x. the interest gained from the 6% account is 0.06x, for the 7% account, it is 0.07x and from the 8% account, it is 0.08x. thus we have
0.06x + 0.07x + 0.08x = 52.50
you can solve for x and hence find the total investment