I posted recently about calculating subnets and CIDR notation quickly, but I didn’t mention in that post host to quickly get the Network ID, first host and Broadcast address for a subnet given an awkward address. This is another easy trick that covers that!
A friend of mine mentioned recently that he has to work out subnet masks in his head for an exam and commented in reality he’d just use a subnet calculator. Whilst this is probably true, there’s a quick trick that might help if you’re calculating subnets under duress. This isn’t a full write up and offers no real explanation of why it works, it’s just pointing out a trick you may have missed which might come in handy one day!