math
posted by chanell on .
Mr. Wilson invested money in two accounts. His total investment was $40,000. If one account pays 4% in interest and the other pays 8% in interest, how much does he have in each account if he earned a total of $2,720 in interest in 1 year?

invest x at 4%, y at 8%
x + y = 40000
.04x + .08y = 2720
.08x + .08y = 3200
.04x + .08y = 2720
now subtract:
.04x = 480
x = 12000
y = 28000
.04*12000 + .08*28000 = 480 + 2240 = 2720 
x + y = 40,000
.04x + 0.08y = 2,720
x = 40,000  y
.04(40,000  y) + 0.08y = 2,720
1,600  .04y + 0.08y = 2,720
1,600 + 0.04y = 2,720
0.04y = 1,120
y = 28,000
x = 40,000  28,000
x = 12,000
y = 28,000