5 cool math tricks ft. Technicality

The tip on tipping can be thought of or said differently.  Rather than thjnking "move the decimal place left one place" think "divide by 10" .  Where Z is the total.cost, a 20% tip is Z divided by 10 times 2.   [ ($170/10 = $17) X 2 ] = $34].  Moving the decimal point left 1 space is dividing by 10.  To me "dividing by 10" is a quicker and easier way to think of it.  But, neither is wrong.  And if you simplify the equation, a 20% tip really is just Z divided by 5, which is even easier on some totals.  A total of $55.  The 20% tip is $11.  I usually round the dollar value to the nearest number ending in 0 or 5 and divide by 5, which gives either a >19%, 20%, or <21% tip.  I figure close enough.  So, $173 = Roundedup$175/5 = $35 tip, a little over 20%.  $172 = roundedDown$170/5 = $34 tip.  A little lower than 20%.  How much lower?  An exact 20% tip on $173 is $173/5 = $34.60.  The rounded down tip is $34.  So the rounded down tip is 60 cents less than an exact 20% tip.  But its still more than a 19% tip.  An exact 19% tip on $173 = $32.87.  So the rounded down tip of $34 is $34 - $32.87= $1.13 greater than a 19% tip.  So the rounded down tip is $0.60 less than 20% tip and $1.13 greater than 19% tip.  I figure close enough, and also my karma probably averages out between the round-up tips and round-down tips over time.  😁. Wow!  Now that was a very satisfying nerdification exercise on my part.  Sorry.  Your channel covers physics and math.  A nerd magnet.