Question 54683
1st: x+y = 500
2nd: 0.09x+20 = .11y 
Multiply 2nd by 100 to get:
3rd: 9x-11y=-2000
Multiply 1st by 9 to get:
4th: 9x+9y=4500
Subtract 3rd from 4th to get:
5th: 20y=2500
Then y=125
Substitute that into 1st to solve for "x", as follows:
x+125=500
x=375
Check this answer in 3rd:
9(375)-11(125)=-2000
2000=2000
It checks.
Answer: x=375; y=125
Cheers,
Stan H.