A businessman has $1000 income from bonds bearing 4% and 5%. If the amounts invested at 4% and 5% were interchanged, he would earn $50 more annually. Find the total amount invested by the businessman.

Answer 1

amount invested at 4% --- x
amount invested at 5% ---- y

.04x + .05y = 1000
4x + 5y = 100000 , #1

reversed:
.05x + .04y = 1050
5x + 4y = 105000 , #2

solve these two equations.