Word Math Problem

Question

A college student earned $7,800 during summer vacation working as a waiter in a popular restaurant. The student invested part of the money at 9% and the rest at 8%. If the student received a total of $654 in interest at the end of the​ year, how much was invested at 9% question mark

Answer 1

Let X = amount invested at 9%

Let 7.8K-X = amount invested at 8%

Let K = $1000

.09X + .08(7.8K-X) = 654

multiply by 100

9X + 8(7.8K-X) = 65.4K

X = 65.4-62.4 = 3K = $3000 at 9%

7.8K-3K = 4.8 = $4,800 at 8 %

That's .09 x 3000 + .08 x 4800 = 270 + 384 = $654