I do this too. Also, I was so terrible at the "speed and accuracy" (which was really speed) tests in the early elementary years that it was basically assumed I had no math ability at all, an assumption I did not actually think to question until many, many years later.

(I will note that my father, who was a quite competent physicist, was considerably worse at that sort of speed calculation/memorization than I was. He also essentially saw the world in mathematical terms much of the time as far as I could tell.)