And I wonder how many maths teachers know the number of children in their class each session through the day?

It makes you smart.

@Gwendolyn2018 I have views about such people. My editor routinely corrects what I send him for publication, and I am delighted that he does so.

As a matter of routine to achieve what?

@Gwendolyn2018 That is their issue, not yours. Thank you for promoting the value of clarity of writing.

@Gwendolyn2018 I will, but I will do so gently and supportively.

Ask @anglophone, he is a genius.

@Betty Two simultaneous equations in two unknowns. Can also be represented by an order 2 square matrix which probably has a non-zero determinant, thus allowing a solution to the equation Ax=b. Are you happy now?

@anglophone No, I am not happy. What is the answer?

@Betty What? You expect me to actually crunch the numbers? You are asking far too much of me! GRIN!

@anglophone Does that mean you don't know the answer? How disappointing. I was really looking forward to you showing of a little.

@Betty My exhibitionism is of the NSFW variety, not the nerd variety.

1 apple costs 30c., 1 plum costs 20c.
Therefore 3 apples 90c + 2 plums 40c = $1.30
2 apples 60c + 3 plums 60c = $1.20.

No wanking words, formula or NSFW varieties just trial & error, practicality plus astute observation that anything more complex would not be attempted by Petter.

@FrayedBear You used subconscious algebra to find the solution.
The word derives from the Arabic "al jabr" implying repair of what is broken or missing". Mathematical algebra is just a set of techniques to aid the task.

@Petter I doubt it Petter as I doubt that I could have solved it if the individual prices had been greater, say $1.57 for apples & $1.27 for plums. . .$7.25 vs $6.95.
Fascinating etymology. Has the word been in the English language since the crusades or earlier?

@FrayedBear The renaissance was simply the re-birth of knowledge in Christian Europe. The lost European knowledge had, fortunately, been preserved and even developed by the Islaamic scholars of the Moorish kingdoms, who were not constrained by religious dogma and thus always ready to accept new ideas.
Hence, the many Arabic words (usually starting with al) that entered science. "Al" is the Arabic equivalent of "the".
Alkali in chemistry, for example. A substance which was obtained from calcined ashes. (Potash). Alcohol is another.

@Petter Curious that a substance banned in their religion is named by them but had been long consumed by xtians. . . . Xtians so stupid they didn't know that wine, beer & cider have a common ingredient that makes their legs wobble & speech slur?

@FrayedBear Alcohol was well known and liked, (too much liked!) in the Middle East long before Islaam. That is why the religious killjoys banned it. Not that it stops any Middle-Easterners from heading into the nearest Emirate and getting pissed.

@Petter I had an alcoholic Indian acquaintance who boasted of having to travel a thousand klms to get a drink in another state. Having just checked the net I see that alcoholism is a problem with Punjab's.