Question 1138669
A $132,000 trust is to be invested in bonds paying 8%, CDs paying 6%, and mortgages paying 10%. The bond and CD investment together must equal the mortgage investment. To earn a $11,200 annual income from the investments, how much should the bank invest in bonds?
<pre>Let amount invested in bonds, CDs, and mortgages be B, C, and M, respectively
Then we get: B + C + M = 132,000 ------ eq (i)
Also, B + C = M ------- eq (ii)
And, .08B + .06C + .1M = 11,200_____2(.04B + .03C + .05M) = 2(5,600)_____.04B + .03C + .05M = 5,600 ------- eq (iii)

2M = 132,000 ------ Substituting M for B + C in eq (i)
{{{matrix(1,5, M, "=", "132,000"/2, "=", "$66,000")}}}, and so, B + C = 66,000 ======> C = 66,000 - B
.04B + .03(66,000 - B) + .05(66,000) = 5,600 ------ Substituting 66,000 - B for C, and 66,000 for M in eq (iii)
.04B + 1,980 - .03B + 3,300 = 5,600
.04B - .03B = 5,600 - 5,280
.01B = 320
Amount invested in bonds, or {{{highlight_green(matrix(1,5, B, "=", 320/.01, "=", "$32,000"))}}}