Moment of inertia question If we have five identical rigid rods, each of length l and mass m, are connected together to form the system shown in the figure. The system may rotate about an axis passing through AB.
The question is to find the moment of inertia of the system with respect to axis AB.

So what I did considered BC as a rod rotating about its end. I then considered DC as a mass connected to BC (but I doubt this one)
And the rest I do not know how to consider them. I would appreciate some guidance on how to think of moment of inertia in this problem. 
 A: The missing piece you need is The Parallel Axis Theorem, which is incredibly useful for calculating moments of intertia in general.  Let us know if you still have specific issues (e.g. how to implement this).

Edit:
The simple equations for moments of inertia for individual objects (e.g. $I = \frac{1}{3} m L^2$ for a rod about its end) are specifically with respect to a certain axis of rotation.  The difficulty is when you need to know the moment of inertia about a different axis.
For example, the moment of inertia for $DE$ could easily be calculated if it was rotating about the line $CD$ --- it would just be $I_{DE,0} = mL^2/3$.  But we want to know what it is about the line $AB$ instead --- so we use the Parallel Axis Theorem, 
$$I = I_0 + mx^2$$
(for an offset distance $x$, which in this case is the length of the rod $BC$, so $x=L$.  Thus, for the moment of Inertia of $DE$, about $AB$ is:
$$I_{DE} = mL^2/3 + mL^2 = 4mL^2/3$$
Note that this works because the original axis of rotation ($CD$) is parallel to the new axis of rotation ($AB$).
