Now this is an interesting topic. There was a time immediately after hurricane Wilma when in my area we lost all power for about 17 days. There was really nothing to do. It was extremely quiet outside, as there was little to no automobile traffic because there was no gas. The roads were strewn with tree limbs and debris and many were impassable. So, when I say, there was nothing to do, you didn't want to do anything. The daytime temperatures got up to the mid to high 90's. You could stand still and just sweat.
I found at that time what a perfect time to practice doing math in my head. I could just sit outside under the shade of what was left of a huge Avocado tree and practice additions and subtractions. My methods were a lot like yours. I used a simple step by step evaluation that fell in place.
I will say if it gets too difficult you could use the binary system and then you'll only have zeros and ones to deal with. But, if you really want to stimulate your mind, use the octal, or hexadecimal system. Like I said, that there wasn't anything to do, and if I made a mistake, it didn't matter a hill of beans. I could just erase my mental image and start over. A wrong answer didn't create any disasters.
But, if I'm figuring out a woodworking or cabinet layout, a wrong answer could wind up with a kitchen countertop that's 6' high, and wall cabinets 6" high, and instead of fitting on a wall that's 7' long they end up 17' long. So, what was the consequence of making a mistake. Lets see...lost time, material waste, and aggravation. If it's necessary to do any math, I write everything down so I have a record of what the details are and what they apply to. I don't do any project planning and proceed without making a drawing of some sort.
It does seem very simple to start a project with what's in our mind. But having some reference to back up our thoughts might be easier than trying to remember all the numbers. As for your despair with division,
try this method.
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