I will try and explain some practical issues that occur when using mathematics in finance. I will focus mostly on the Black-Scholes model and time series predictions. I will try and do this in an informal manner. Time permitting, I will try to defend the field of quantitative analysis from the charge that it caused all the economic problems associated with the economic downturn. I may even have a few kind words for high frequency trading. This talk will be an attempt by the speaker to reconcile his love of mathematics with his love of trading and discuss some avenues in which the two disciplines meet.