Question

Sally has $40,000 to invest some money at 9% interest and the rest at 11%. If her total annual income from these two investments is $4,300, how much does she invest at

Answer 1

a = amount invested at 9%

b = amount invested at 11%

`\bf \begin{array} \cline{1-1} \textit{a\% of b}\\ \cline{1-1} \\ \left( \cfrac{a}{100} \right)\cdot b \\\\ \cline{1-1} \end{array}~\hfill \stackrel{\textit{9\% of`

we know she has a total of $40,000 to invest, so, if she invested "a" amount in one, the other quantity must be the slack left from 40,000 and "a", namely b = 40000 - a.

we also know that the yield or earned interest from both amounts is 4300, thus

`\bf \stackrel{\textit{yield of`