Answer:
a) Current stock price = $50
45*(1+r)^2 = 50
(1+r)^2 = 50/45
r = [tex]\sqrt{50/45}[/tex] -1
r = 0.05409255
r =5.41%
b )When the margin is 50%, 50% is paid by broker
Price paid = 50% *45 = 22.5
Price received from broker = 50% * 45 = 22.5
Current price of share = 50
Profit made per share = 50 - 45
Profit made per share = 5
Therefore 22.5*(1+r)^2 = 22.5 + 5
22.5 *(1+r)^2 = 27.5
(1+r)^2 = 27.5/22.5
1+r = [tex]\sqrt{27.5/22.5}[/tex]
r = [tex]\sqrt{27.5/22.5}[/tex] - 1
r = 1.1054 - 1
r = 0.1054
r = 10.54%