Question 620904
let us say that the amount invested in the 6% fund is x. Therefore the amount invested in the 4% fund is 1800-x

Let us change the % to a value, so 4% can be written 4/100 = 0.04 and 6% can be written 0.06

Now we multiply the interest rate by the amount invested for each fund which added together equal $80:

0.06(x) + 0.04(1800-x) = 80

solve for x:
0.06x + 72 - 0.04x = 80
0.02x = 8

To find x divide both sides by 0.02:
0.02x/0.02 = 8/0.02

x = 400

So the amount invested at 6% rate was $400 and therefore the amount at 4% was $1400

To check we multiply the amount invested by the interest rate for each and added together we should get $80

0.06(400) + 0.04(1400) = 80 !!!