Answer:
After 45.7 years
Step-by-step explanation:
∵ r = 1/2% per year
∵ P0 = $40
∵ Pn = $50
∵ Pn = P0 ( 1 + r/100)^n-1
∵ P0 is initial value , Pn is the value after n years , is the rate
∴ 50 = 40 (1 + 0.5/100)^n-1
∴ 50/40 = (1.005)^n-1
∴ 1.25 = (1.005)^n-1 ⇒ insert ln in both sides
∴ ln(1.25) = (n-1)ln(1.005)
∴ n - 1 = ln(1.25)/ln(1.005)
∴ n = ln(1.25)/ln(1.005) + 1 = 45.7 years
