The answer is 1690. First find
the amount of interest by a single investment by multiplying the investment
amount by the percent interest in decimal form. Then calculate the total by
adding up all the products of investment times interest. Matrices will allow to
multiply two things together and add the products up all at the same time. So
we need to find the investment matrix and interest matrix.
Investment matrix A (transposed) = (a1 a2 a3) = (13,000 12,000 4,000)
Interest Matrix B = (b1
b2 b3) = (0.05 0.06 0.08)
Amount of interest earned = a1b1 + a2b2 + a3b3
Amount of interest earned = (0.05) (13,000) + (0.06)
(12,000) + (0.08)(4,000)
Amount of interest earned = 1690
