Hi Carl
Can I ask what study material you are using for your Cisco studies? IMHO the best resource I have found for subnetting is the Sybex book "Cisco Certified Network Associate" by Todd Lammle.
I had read some different resources on subnetting before I picked up this book and altough I understood subnetting, this book explained it in a way I found easy to understand and helped me get to the point that I can subnet in my head quickly. This is a skill that will be invaluable on exam day.
Even if you can not afford to purchase this title at present, I would recommend you check if you can rent if from your local library.
I have attached a document that I put together based on the material in Todds Sybex book. I am not sure how helpful this is going to be if you do not understand the teaching behind this.
I would urge you, that if you are serious about a career in IT/Networking then don't look for shortcuts, as you are only doing yourself a disservice. Get some reputable material to study and keep going over it until you know and understand it. This may take a little longer, but in the long run your will be a more knowledgeable network engineer and a valuable employee.
HTH
Best Regards,
Michael
