Question 634366
A man makes three investments totaling $24000 with the interest rates at 6%, 7% and 8%. The total annual income is $1720, and the income from the 7% investment is $4o less than the combined income from the other investments. Find the amount of each investment.
ans:-
let his investment & income out of that is as follows
    investment$         rate       income$
    say x               6%=.06     .06x
    say y               7%=.07     .07y
    24000-(x+y)=z say   8%=.08     .08z
----------------------------------------
total=24000                        1720
so .06x+.07y+.08z=1720------eqn 1
&  .07y+40=.06x+.08z  ------eqn 2
from above 2 eqns .06x+.08z =.07y+40=1720-.07y
or 2 * .07y=1720-40=1680
or y=1680/.14=12000
now from eqn 1
.06x+.07*12000+.08(24000-x-12000)=1720
or(.06-.08)x=1720-.07*12000-.08*12000=1720-1800=-80
or -.02x=-80
or x=80/.02=4000
now z=24000-12000-4000=8000
so his invesments are $4000,$12000,$8000 (ans)