Question

after winning $280,000 in the lottery, maurika deided to place the money in three different investments : a certificate of deposit paying 4% , a money market certificate paying 5% , and some Aa bonds paying 7%. After 1 year she earned $15,400 in interest. find how much was invested at each rate if $20,000 more was invested at 7% than at 5%

Answer 1

Invested $X at 5%.
Invested x+20,000 at 7%.
Invested 280,000-(x + (x+20,000)) = 280,000 - 2x - 20,000 = -2x + 260,000
at 4%.
In each case, I = P*r*t.
I = x*0.05*1 + (x+20,000)*0.07*1 + (-2x+260,000)*0.04*1 = 15,400.
0.05x + 0.07x+1400 + (-0.08x)+10,400 = 15,400,
0.12x - 0.08x + 11,800 = 15,400,
X = $3600 at 5%.
x + 20,000 = 3600 + 20,000 = $23,600 at 7%.
-2x + 260,000 = -7200 + 260,000 = $252,800 at 4%.