Question

A mother earned $​8750.00 from royalties on her cookbook. She set aside​ 20% of this for a down payment on a new home. The balance will be used for her​ son's future education. She invests a portion of the money in a bank certificate of deposit​ (CD account) that earns​ 4% and the remainder in a savings bond that earns​ 7%. If the total interest earned after one year is ​$420.00​, how much money was invested at each​ rate?

Answer 1

The problem statement is not clear regarding which money is invested. We will assume it is the 80% of $8750 that is set aside for future education. That amount is

... 0.80 × $8750 = $7000

If x represents the amount invested at 7%, then the total interest earned is

... (7000 -x)×4% + (x)×7% = 420

... 280 +0.03x = 420

... x = 140/0.03 ≈ 4666.67

$4666.67 was invested at 7%.

$2333.33 was invested at 4%.