For a radioactive material, its activity A and rate of change of its activity R are defined as A=−dN/dt and R=−dA/dt, where N(t) is the number of nuclei at time t. Two radioactive sources P (mean life τ) and Q (mean life 2τ) have the same activity at t=0. Their rates of change of activities at t=2τ are RP and RQ, respectively. If RP/RQ=n/e, then the value of n is