Equal amounts are invested at 5%, 7%, and 9% annual interest. If the three investments yield a total of $777 annual interest, find the total investment.

Answer 1

The annual interest is P x I where P is the principal and I is the interest.

Three equal investments, let's call them P are invested at 5% 7% and 9%

The interest on each loan, P x I becomes P x .05, P x .07 and P x .09

If the total is $777, the equation for the sum is: $777 = .05P + .07P + .09 P

$777 = .21P

P = $3700 for each investment.

Answer 2

Let P = the amount invested

Then,

.05P + .07P + .09P = 777

.21P = 777

P = 3700 or the total investment is $3,700.