Word problem question about investments

Question

I've been having trouble with this word problem and wondered if anyone could shed some light. If you could explain how it's done, that'd be great! Thanks!

 

A mother wants to invest $15,000.00 for her son's future education. She invents a portion of the money in a bank certificate of deposit (CD account) which earns 4% and the remainder in a savings bond that earns 7%. If the total interest earned after one year is $900.00, how much money was invested in the CD account?

Answer 1

Let x be the amount invested in the CD.

 

Let y be the amount invested in the savings bond.

 

x+y=15000

 

.04x + .07y = 900

 

Multiply the first equation by -.04 and add it to the second equation to get rid of the x term.

 

-.04x-.04y = -600  add this equation to the second equation.

 

.03y = 300  multiplying by 100.  3y = 30000

 

dividing by 3 on both sides: y = 10000.  So x = 5000

 

So she invested 5000 in the CD account