I usually try doing it in my head first. I use paper if it is available. I use a calculator when I don’t have time, or fail at the first two steps.

I noticed my number skills were deteriorating without proper use, and I found that alarming. I’m still weaker than I used to be, but not as bad as I was.

It’s just important to think for ones self when one can. The brain is a muscle that atrophies without use.