Question 1177782
An investor has 40000 dollars to invest. If part ismple interest rate and the rest at 11%, how much should at each rate to yield 8% simple interest on the total amount? Give the part, which is invested at the 7% interest rate 

Let x be  invested at 7% 
and y be  invested at 11%

total yield = 8% = 8%*(x+y)

x+y =40000 ----------------1
7%x+11%y = 8% (x+y)
multiply by 100

7x+11y=8(x+y)

7x+11y=8x+8y
-x+3y=0 --------------------2

add 1 &2

4y=40000
y= 10000
x=30000

$30,000 is invested at the 7% interest rate