up down sampling and low-pass filters I am trying to figure out what seems very trivial thing about down sampling and up sampling. The problem that I am facing is how to find the effects of up sample on a signal followed by a filter and/or a filter followed by down sampling. Here is a problem related to this from the Oppenhiem and Schafer book.

 

I am trying to see what happens to x[n] after it pass the hlp[n], considering that hlp[n] has wc = pi/4. Will there be a gain on this or just the frequency is affected? 

Please help, Thanks in advance
I think, this will act like low pass filter with $\pi/2$ instead of $\pi/4$ cutoff frequency