Morgan invested $4,200 into two accounts. one account paid 4% interest and the other paid 7.5% interest. she earned 7% interest on the total investment. how much money did she put in each account?

The amount invested at 4% was $600

The amount invested at 7.5%  was $3,600

Step-by-step explanation:

Let

x ----> the amount invested at 4%

$4,200-x -----> amount invested at 7.5%

we know that

The total interest earned is equal to the interest earned by the amount invested at 4% plus the interest earned by the amount invested at 7.5%

Remember that

so

The linear equation that represent this situation is

Solve for x

therefore

The amount invested at 4% was $600

The amount invested at 7.5%  was $3,600

because linear equations are a lot simpler than quadratics equations, and linear equations formula is a lot easier to memorize. that's why i think they're harder.