1. The problem statement, all variables and given/known data This time I'd like someone to verify that my rationale behind the correct answer is accurate... Which of the following will decrease the chance of turbulent blood flow in a vein? A. Narrowing the vein. B. Thinning the blood without changing its density. C. Increasing the absolute pressure on each end of the vein by the same amount. D. Lowering the blood density without thinning it. Correct Answer: D. 2. Relevant equations Reynolds number (NR): NR = (2ρvR)/η where ρ is density, v is the average velocity, R is the vessel's radius, and η is viscosity. 3. The attempt at a solution Okay... I know a fluid with Reynold's number less than 2000 is results in laminar and non-turbulent flow. Of course I see why D is absolutely correct because a drop in density without changing it's viscosity will decrease NR, but what about choice A as well?! if I decrease the radius I should get the same effect right? ...OR! (I just had an epiphany) because flow rate *must* remain the same (Q=Av), decreasing the radius would only increase the velocity, thus there would be no change. What do you think?