Question 5892
You can check your answer by multiplication:
.06*3999.60 = 239.976
.09*5999.40 = 539.946
239.976+539.946 = 779.922 - not a correct answer because it should only total $684:

Let x = the amount jodi invested at 6%
.06x = the interest earned at 6%
Let 10000-x = the amount invested at 9% ($10000-the amount invested at 6%=the amount invested at 9%)
.08(10000-x)= the interest earned at 9%
6% interest + 9% interest = $684
.06x+.09(10000-x)=684
.06x+900-.08x=684
-.03x=684-900
-.03x=-216
x=7200
amount invested at 6%=7200
amount invested at 9% = 2800 (10000-7200)

check:
.06*7200=$432
.09*2800 = $252
432+252=$684