Last year Lisa had 10000 to invest She invested some of it

Last year, Lisa had $ 10,000 to invest. She invested some of it in an account that paid 5% simple interest per year, and she invested the rest in an account that paid 10 % simple interest per year. After one year, she received a total of $ 650 in interest. How much did she invest in each account?

Solution

Say she equated x at 5%
and the remaining (10000 - x) at 10%

x at 5% will result in 5/100 of x = 0.05x dollars of interest

10000 - x at 10% will result in 10/100(10000 - x)
or 0.1(10000 - x)
or 1000 - 0.1x dollars of interest

Now, total interest is 650

So, equation becomes :
0.05x + 1000 - 0.1x = 650
1000 - 0.05x = 650
0.05x = 1000 - 650
0.05x = 350
x = 350 / 0.05
x = 7000

So, she invests $7000 at 5%
and 3000 at 10%