Doubling both arrival and service rates in M/M/1 halves the average wait

Consider the following two M/M/1 queueing systems where: In $Q_1$: arrival rate $\lambda$, service rate $\mu$. In $Q_2$: arrival rate $2\lambda$, service rate $2\mu$. Let $W_1$ and $W_2$ be the average waiting times of an arriving customer in $Q_1$ and $Q_2$ respectively. Then: