Question

You buy $10,200.00 in stock A and stock B, paying 5.3% and 7.1%, respectively. If the interest you earned for the year was $640, how much was invested in stock A and how much in B?

Answer 1

I found:
`A=$4,677.8`
`B=$5,522.2`

Explanation:

Call the two (stock) money amounts invested `A` and `B`, so you have:
`A+B=10,200`
`0.053A+0.071B=640`

From the firs you get:
`A=10,200-B`
Substitute into the second:
`0.053(10,200-B)+0.071B=640`
`540.6-0.053B+0.071B=640`
`0.018B=99.4`
`B=99.4/0.018=$5522.2`
Giving for A:
`A=10,200-5522.2=$4677.8`