Question

Angelo invested $4,000 into two accounts. One account paid 4% interest and the other paid 9% interest. He earns 6% interest on the total investment. How much money did he put in each account?

Answer 1

Answer:

$2,400 was placed in the account earning 4%, and $1,600 was placed in the account earning 9%

Explanation:

In this case, we have two unknowns, so in order to be solved, we need to find two equations.

We know that amount 1, that we call x, plus amount 2, we call y, is 4000.  

x + y = 4000

Also we know, when we add the interest earned on amount 1 to the interest earned on amount 2, the total interest is 6% of 4000, it means: 240

0.04x+0.09y=240

So, we have two equations with two unknowns

x + y = 4000

0.04x+0.09y=240

That we can solve for any method we know. We will use substitution.  Lets clear from first equation the unknown x.

x=4000-y

Then, we substitute in second equation

0.04(4000-y)+0.09y=240

And we solve:

160-0.04y+0.09y=240

0.05y=240-160

y=80/0.05=1600

Now we simply plug this into our first equation and solve for x

x+y=4000

x+1600=4000

x=4000-1600

x=2400

So, $2,400 was placed in the account earning 4%, and $1,600 was placed in the account earning 9%