Calculating interest

Question

Last year, Justin had $20,000 to invest. He invested some of it in an account that paid 8% simple interest per year, and he invested the rest in an account that paid 7% simple interest per year. After one year, he received a total of $1,560 in interest. How much did he invest in each account?

Answer 1

a + b = 20,000 

.08a + .07b = 1560

 

a = 20,000 - b

.08(20,000 - b) + .07b = 1560

1600 - .08b + .07b = 1560

.01b = 40

b = 4000

 

a = 20,000 - 4000 = 16,000