Abacus - a calculation tool dating back to ancient China and Korea. The first thing which pops into my mind whenever I happen to encounter numbers. Because my brain always goes to that thought, I have spontaneously taken it for granted as a way of doing a mental calculation. Therefore, I do not even know what comes up first in another's head when facing a mathematical problem.
Would this way be still faster than other ways? Yeah, it used to be but not exactly now since I haven't practiced answering complicated questions consisting of many digits in a set for a while. Need to buy an abacus from Amazon today and get my calculation skills back to its genius-level like it used to be.