Mnemonic to find how many Hosts in a Subnet

Hi

I’m teaching our trainees how to find how many Hosts in a Subnet by mental arithmetic as they need it for School.
This is the way I learned how to.

Example Question:
If I need 50 Hosts in the 192.168.1.0 Range.

1. Step: 50 + 1 = 51
2. Step: 2 Power of 6 will fit = 64
(64 - 2 = 62 Hosts can be used)

Now if I need to find how many Subnets:
3. Step: 8 (total) - 6 (2 power of 6) = 4 Subnets

Is this the easiest way? Alternatively, do you have any other better mnemonic’s?

Many thanks in advance