Question

Mr. Jackson invested a sum of money at 6% per year, and 3 times as much at 4% per year. How much did he invest at each rate if his annual return totaled $144

Answer 1

Answer:

x + y = 1200  →  (1)   ("A man invested a total of $1200 into two accounts")

0.04x + 0.06y =57 → (2)   ("The total interest earned was $57")

Thus you have the system of 2 equations in 2 unknowns.

You can solve it using the substitution method.

For it,

express y = 1200-x from the first equation and substitute it into the second equation.

You will get

= 0.04x + 0.06*(1200-x) = 57,

= 0.04x + 72 - 0.06x = 57

= -0.02x = 57 - 72 = -15  

=  x = -15/-0.02 = 750.

So, $750 was invested at 4% and the rest  $1200 - $750 = $450 was invested at 6%.

Check.  

0.04*750 + 0.06*450 = 57 dollars.  

∴ $750 was invested at 4% and $450 was invested at 6%.