Merry had $20,000to invest. she invested part of this money in bonds paying 10% annual simple interest and the rest of the money in a saving account giving 5%annual interest. at the end of the year she received $1,800 as extra income how much money did merry place in the savings account?

20,000-x(bonds 10%)=savings (5%) or
20,000-x=y
(x times 10%) + (y times 5%) = 1,800
x/10+y/20=1,800
y=20,000-x
x/10+(20,000-x)/20=1,800
multiply x/10 by 2/2 and add to get
2x/20+(20,000-x)/20=1,800
(2x+20,000-x)/20=1800
(x+20,000)/20=1800
multiply both sides by 20
x+20,000=36,000
subtract 20,000 from both sides
x=16,000
20,000-x=y
y=4,000
16,000 in bonds
4,000 in savings