Question

Juan has $21,000 to invest in two accounts that pay simple interest on an annual basis. One account pays 3% in simple interest, and the other pays 6% in simple interest. How much would she have to invest in each account to earn a total interest of $690 after on year?

Answer 1

2 accounts
x is 1st account
y is 2nd account

both accounts added equal 21000

so
x+y = 21000

account one is that amount times 3% or .03
account 2 is amount times .06

which equals total interrest or 690

so
.03x + .06y =690

the systems equation-solve for x or y and plug the answer back in to get the other variable
x+y = 21000
.03x + .06y =690