Interest rates?

Question

Jes wants to borrow $600 for a new game console and some games. Best Buy has a financing option where she can get everything today for zero dollars but has to pay $675 in 9 months. What is the annual interest rate for this loan?

Answer 1

i = p * r * t

25 = 600(r)(0.75)

25 = 450r

0.055 = r

Answer 2

675 = 600(1 + r/12)^12(0.75)

675/600 = (1 + r/12)⁹

(9/8)^1/9 = 1 + r/12

r = (9/8)1/9 - 1

r = 12[(9/8)^1/9 - 1]

r = 0.16

16%

Answer 3

i = p * r * t

75 = 600r(0.75)

75 = 450r

0.16666 = r