Question 33132
Let's assume that Dave invested $x at 18% and the remainder ($17,000 - $x) at 4%.
The interest earned on the $x is: 18% of x
The interest earned on the remainder ($17,000 - $x) is: 4% of ($17,000 - $x).
The sum of these two amounts is: $1,380

So, if you change the percents to their decimal equivalents, you can write the equation which can then be solved for x.

{{{0.18x + 0.04(17000-x) = 1380}}} Simplify and solve for x.
{{{0.18x + 680 - 0.04x = 1380}}} Combine like-terms.
{{{0.14x + 680 = 1380}}} Subtract 680 from both sides of the equation.
{{{0.14x = 700}}} Divide both sides by 0.14
{{{x = 5000}}}

Dave invested $5,000 at 18% interest and ($17,000 - $5,000) $ 12,000 at 4% interest.