A stock price has an expected return of 9% and a volatility of 25%. It is currently $40. What is the probability that it will be less than $30 in 18 months? Please show 'step by step'. I keep getting 12.234 and I know it's a simple calculation error. Is ln(40/30) = .2784?? Maybe this is where I'm messing up. Also, is it possible to put this equation into excel? Thank you..