# DE: Unit Cancellations Not Making sense

by dillonmhudson
Tags: cancellations, sense, unit
 P: 50 1. The problem statement, all variables and given/known data Consider a tank used in certain hydrodynamic experiments. After one experiment the tank contains 200 liters of a dye solution with a concentration of 1 g/liter. To prepare for the next experiment, the tank is to be rinsed with fresh water flowing in at a rate of 2 liters/min, the well-stirred solution flowing out at the same rate. Find the time that will elapse before the concentration of dye in the tank reaches 1% of its original value. 2. Relevant equations $$\frac{dQ}{dt}$$=rate in - rate out 3. The attempt at a solution Why the heck do they cancel units incorrectly?
 Sci Advisor HW Helper Thanks P: 25,160 Hard to say until you tell us what the heck Q is.
 P: 50 Q is the amount of dye in the tank. dQ is the rate of change of the amount of dye in the tank.