I just love the way that we Australians, in this industry are anal about the really important stuff like whether someone who uses a wizz wheel has higher moral ground than someone who uses a calculator, and whether someone who uses neither can claim themselves victorious.
Well I sneer upon you loathsome, dare I say unsafe masses, as I claim moral superiority; you see I have a wiz wheel on my over-sized Pilot watch which trumps you all.
As if my overt strutting wasn't enough, one glance at my watch by all and sundry, tells the great unwashed that I am a Pilot without having to actually say a word. This coupled with Ray-bans at a bar lets all those in "visual contact" make no mistake. I use words like "aircraft" instead of "plane" and extol the virtues of hand flying and make anti- automation comments whenever possible to mask my fear of it and the fact that I'm not really sure of what it all does.
Sometimes on a long flight I like to turn everything off and hand-fly my jet based on nothing more than memorised maps, pure skill and my trusty watch wizz wheel; usually after announcing "watch this". The fact that I can do this whilst complaining about Y gen (of which I am not) and randomly ranting about the government, single mothers, Airline management etc asserts my authority and prowess in the cockpit.
As for mental math tricks:
Multiplying by 5, 25, or 125
Multiplying by 5 is just multiplying by 10 and then dividing by 2. Note: To multiply by 10 just add a 0 to the end of the number.
12x5 = (12x10)/2 = 120/2 = 60.
Another example: 64x5 = 640/2 = 320.
And, 4286x5 = 42860/2 = 21430.
To multiply by 25 you multiply by 100 (just add two 0's to the end of the number) then divide by 4, since 100 = 25x4. Note: to divide by 4 you can just divide by 2 twice, since 2x2 = 4.
64x25 = 6400/4 = 3200/2 = 1600.
58x25 = 5800/4 = 2900/2 = 1450.
To multiply by 125, you multiply by 1000 then divide by 8 since 8x125 = 1000. Notice that 8 = 2x2x2. So, to divide by 1000 add three 0's to the number and divide by 2 three times.
32x125 = 32000/8 = 16000/4 = 8000/2 = 4000.
48x125 = 48000/8 = 24000/4 = 12000/2 = 6000.