Question

A principal of $2500 is invested,part at 8% per annum and the rest at 12% per annum. In a year, the 8% investment interest was doubled the 12% investment interest. How much invested at each rate? Express in the form Ax+By=C

Answer 1

amount invested at 8% ---- x
amount invested at 12% --- y

x+y = 2500

.08x= 2(.12)y = .24y
times 100
8x = 24y
x = 3y
sub into the 1st
3y + y = 2500
4y = 2500
y = 625
then x = 1875

$1875 were invested at 8% and 625 were invested at 12%

check:
.08(1875) = 150
.12(625) = 75
we can see that 150 is twice 75