I'm studying for the Network + test, and for subnetting, I don't have a problem subnetting class C networks, but I'm confused on class B.
the method the book I'm using is to ask 5 questions
how many subnets - the formula is 2 to the X power - x = number of masked bits - no problems there
how many hosts per subnet - formula is 2 to the Y power minus 2 y = number of host per subnet
what art the valid subnets formula is 265 - subnet mask = block size aka increment number - now this is what throws me,
so, for example, if i have a class B network and the mask is 255.255.240.0 (/20) i would use the formula
256-240 = 16 so the block size or increment number is 16. in the book, he makes a chart like this

so does this mean that in the first column for instance. if the address is 172.16.X.Y the first host address is 172.16.0.1 and the last address in subnet 0.0 is 172.16.15.254? which means there are LOTS of hosts?

Yes that is exactly what it means... It also measn that 172.16.1.0 and 172.16.2.0 and 3.0, etc.. are all host addresses inside that large block.

Now in the real world you would only carve a class B this large to hand out to sub-organizations where it will be chopped up further. You would never want a flat network that large.

The subnet calculator helps you design networks by taking an IP address and network mask and returning information such as network, broadcast address, and host range.

One of a set of tools we're offering as a way of saying thank you for being a part of the community.

Now in the real world you would only carve a class B this large to hand out to sub-organizations where it will be chopped up further. You would never want a flat network that large.

But you got it!