SOLUTION: An investor received $1400 interest per annum from a sum of money, with part of it invested at 10% and the remainder at 7% simple interest. This investor found that if she intercha

Question 122552: An investor received $1400 interest per annum from a sum of money, with part of it invested at 10% and the remainder at 7% simple interest. This investor found that if she interchanged the amounts she had invested she could increase her return by $90 per annum. Calculate the total amount invested.
Answer by edjones(8007) (Show Source): You can put this solution on YOUR website!
A) .1x+.07y=1400
B) .07x+.1y=1490
.
A)
.1x=1400-.07y
x=14000-.7y multiply each side by 10.
.
B)
.07(14000-.7y)+.1y=1490
980-.049y+.1y=1490
.051y=510
y=10000
.
A)
.1x+.07(10000)=1400
.1x+700=1400
.1x=700
x=7000
.
Check:
B)
.07(7000)+.1(10000)=1490
490+1000=1490 true
.
Ed
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