Enrique invests $6900 in two different accounts

Question

Enrique invests $6900 in two different accounts. The first account paid 9 %, the second account paid 8 % in interest. At the end of the first year he had earned $568 in interest. How much was in each account?

Answer 1

I'm assuming this is simple interest, not compound interest.

in the case of simple interest it is simply:

initial amount*percentage = interest over a year

converting percentage to decimal this means 8% is .08 and 9% is .09

in that case lets set up two account variables x & y

 

the initial total was x + y = 6900

the interest earned was x*.08+ y*.09 = 568

this is a system of equations

 

we can solve this by multiplying the bottom equation by 12.5

giving x + 1.125y = 7100

now subtract the original equation on both sides to get:

.125y = 200

now we solve for y by dividing by .125

y = 1600

thus x = 6900-1600 = 5300

 

So, he invests 5300 in the 8% interest account and 1600 in the 9% interest account.