Hi all. I'm trying to help a friend work a differential equation problem since I've already taken this course and gotten an A in it, but this other problem has me a little confused. The book is ODE's by Tenenbaum and Pollard, chapter 3 lesson 15a number 2. #1) Tank initially holds 100 gal of brine containing 30 lb of dissolved salt. Fresh water flows into the tank at a rate of 3 gal/min and brine flows out at the same rate. (a) Find the salt content of the brine at the end of 10 minutes and (b) When will the salt content be 15 lb? This one I've solved easily but number 2 says, #2) Solve problem 1 if 2gal/min of fresh water enter the tank instead of 3 gal/min. The solution on the next page says it should be (a) x=30(1-.01t)^3 which, when 10 is plugged for t gives 21.87 lb. Can someone explain what I'm missing? Shouldn't the rate in still be zero?