It's too easy to be wrong

I was watching  the Cooked miniseries on somebody else's Netflix account. This is the beautiful set of documentaries [loosely] based on Michael Pollan's book of the same name [prevliers]. In the middle of the second episode, touching on the obesity epidemic, they wheel out Harry Bazler, food pundit, to say "The solution to obesity is to tell people that you can eat what ever they want for dinner - soup, Caesar salad with extra croutons, entrée, dessert with ice-cream; whatever - so long as they made all the dishes themselves, from scratch."  If folks had to work to get food on the table then a) they'd appreciate it all the more b) they wouldn't be bothered because we're all fundamentally lazy. This reminds me of [enormous] comedian [sort of] and singer Harry Secombe's diet "You can eat as much of what ever you want . . . so long as you don't swallow it." Money makes it easy to disconnect the work we put in at the office or driving a backhoe from the handing over wodges of folding-stuff at the supermarket check-out. Sorry, Junior, I had to work for 1h45m to pay for that dorky plastic thing you covet. Same with putting petrol in the car: especially if paid for with plastic.

Same with maths. Back in the days before electronic calculators you had to multiply two numbers by hand: preferably on squared paper. As Minister Agriculture , I have been tasked to find out the total weight of the Irish to plan for next year's food production in the 5 Year Plan of Our Great Leader. I could split 4,757,976 into  999,175 children at [average] 25,125g and 3,758,801 adults at 75,378g; set the numbers up as two long-multiplication sums and add the results:
     3758801    999175
     x 75378   x 25125
     -------    ------
    30070408    losing
   26311607-   thewill 
  11276403--   tolive-
 18794005---  boring!-  
26311607----
------------
283330901778g
But that would take me 6 or 7 minutes. Nope, I'd rather be an engineer about it and round things up and down to get an approximate answer and then add 10% in case next September turns really wet. Something like
Adults = 3,600,000 * 100,000 * 3/4 = 270 billion grams
+kids = 1 million * 25,000 = 25 billion grams.
=300 billion grams
If I was iffy about rounding down the number of adults to 3.6 million I could round them up to 4 million with a weight of 300 billion grams (+25bn for the kids) . . . or I could split the difference.  If students had to work [harrrumph the youth of today etc.] to make such calculations then a) they'd soon learn where they could legitimately cut corners b) they'd be less likely to make ludicrous order-of-magnitude errors about the volume of concrete blocks or a soccer ball or the time it takes a pendulum to swing or the size of things in the real world.  As it is, any maths they see, even easy stuff like €1.49 + 3.99, they switch on their calculator and switch off their crap-detector.

When the aliens from the Planet Zorg come down to harvest the Irish for quality control [prev] before shipping the rest of the humanity off-planet they just want an approximate answer to determine how many space-freighters to send.