Distribution and SDE of a ratio of two Brownian motions
Question
Let and be independent standard Brownian motions and . What is the distribution of for fixed , and what SDE does satisfy?
Short answer
Standard Cauchy at every . and are independent , and cancels in the ratio of two i.i.d. centred normals. Using and , Ito gives (valid while ). The noise can be written as for a single Brownian motion .
Adapted from Joshi, Denson & Downes, Quant Job Interview Questions and Answers, Q3.48, p.85; question and answer rewritten by SelfMadeQuant.com.
See the hint and the full worked solution in the question bank (free account).
Open the worked solutionLessons behind this question
Start with a free lesson: Probability Fundamentals is part of a free topic. Create a free account, no card needed, to read it in full with worked solutions.
Read it free