Whether $y(t) = x(t/3)$ is a memoryless system?
You are trying to mimic what I did at time $t$.  You'll be $y$ for now, say I'm $x$. 

Now suppose that our are mimicking my actions  with your own modification pattern (called $f$), at the very same time. Then, your location, depending on mine, is: 

$$y(t) = f(x(t))\,. $$

Here, you only need the current observation $x(t)$ (hence, no memory). 

Now, suppose that you are trying to mimic what I do at time $t$, but only three times slower ($t/3$). What you will do at $t=3$ (or $y(3)$), I did it at $t = 3/3$, or at one second ($x(1)$). You need memory.