I need help solving this word problem

Question

You invested $18,000 in two accounts paying 4% and 6% annual interest ,respectively. If the total interest earned for year was $800, how much was invested at each rate?

Answer 1

Let's say X is the part of investment earning 4%, and Y earn 6%:

 

0.04 X + 0.06 Y = 800   (4% X => 4/100 X = 0.04 X, and the same with Y). Assuming that $800 was earned in one year)

 

Then you know X + Y = 18000  => x = 18000 - Y

 

replacing in the first equation:

 

0.04 (18000 - Y) + 0.06 Y = 800

 

720 - 0.04 Y + 0.06 Y = 800

 

0.02 Y = 800 - 720

 

Y = 80/0.02

 

Y = $4000

 

If Y = $4000 the rest of 18000 is X = 18000 - 4000

 

X = $14000