If Po dollars are deposited in an account paying r percent compounded continuously and withdrawals are at a rate of 200t (continuously), what is the amount after T years? I derived the formula by taking the limit as m -> ∞ of the compounding interest equation P(t) = Po(1+r/m)^mt which gives us P(t) = Po*e^rt. So including the withdrawal rate - P(t) = Po * e^rt - 200t And that would be the amount in the account after T years. But my question asks, if r = .1 and Po = $5000, when will the account be empty? My function doesn't cross zero, and I don't understand where I made the mistake. Can anyone help me?