A tank with intitial volume [math]V_0[/math] empties according to an exponential law and has volume V at time t given by [math]V = V_0exp(-kt)[/math] Set t = 0 and the values [math]V_0[/math], V and k. Use pen and paper to work out how long it takes for the volume to drop from V0 to V. Show the Solution to see if you are correct.