Walt made an extra $9000 last year from a part-time job. ?

Question

He invested part of the money at 9% and the rest at 8%. He made a total of $770 in interest. How much was invested at 8%?

Answer 1

9% = 0.09

8% = 0.08

x dollars in 8%

So (9000 - x) in 9%

x (.08) + (9000 - x) (0.08) = 770

Solve for x

Answer 2

9x + 8y = 77000

x + y = 9000

multiply second equation by 8

8x + 8 y = 72000

subtraction from first equation yields

x = 5 000 and y = 4 000

so 4 000 invested at 8 percent