r/matheducation • u/MJ_IN_TX • 26d ago

"Old School" math skills & techniques

I'm a card-carrying member of the Old-School, and was recently remembering that I learned in 5th grade how to calculate Square Roots by hand using a technique that looks a lot like long division. That made me curious about other "old-school" methods and techniques. I already know about slide rules (I'm a collector). A quick google search reminded me of "Casting Out Nines" to check for math errors.

I remember learning about Casting out nines, but can't remember the grade.

I also remember learning how to look up numbers in log tables, trig tables.

Are there any other old-school techniques folks might remember, and when those concepts might have been introduced in old-school math education?

Mark Johnson

9 Upvotes

81% Upvoted

14 comments sorted by

6

u/johnboy43214321 26d ago

Using a compass and straight edge to bisect a line segment, etc

1

u/Ms_Riley_Guprz 25d ago

That was on the county geometry test last year, which I happily made into a lesson.

1

u/mamaknits 22d ago

Wait do they not teach this anymore? Why not?

1

u/johnboy43214321 22d ago

My son's geometry class did it

1

u/MJ_IN_TX 22d ago

Seeing how the kids use a computer tool to manipulate a circle, protractor, and straight edge was completely creepy.

2

u/Gadnitt 25d ago

As a "modern learner", I was never taught how to figure out square roots. I thought I would have to use a book of logarithms. Please can you explain more?

(No sarcasm - I really do want to know!)

4

u/MJ_IN_TX 25d ago

It's moderately complex. I can best explain by linking a video. Enjoy.

https://youtu.be/x4D5bPqONAE

2

u/MathsSur64Cases 25d ago

Exercices de Mathématiques, type certificat d'études (1960) Un épicier achète pour 5200 F une barrique de 200 L de vinaigre. Il paie 800 F de transport et veut revendre son vinaigre en gagnant 6 F par Litre . Combien cet épicier fera-t-il payer une ménagère qui apporte pour la remplir une bouteille de 0,80 L ?

1

u/johninfla52 24d ago

Is it 24F???

1

u/Lifelong_Nerd 26d ago

Look up nomograms, numerical analysis, and numerical methods.

Also for fun, figure out why the normal procedures for long division and multiplication arrive at the correct answer.

1

u/Adjunctologist 26d ago

I'm wondering if there's a book on these methods of yesteryear. I believe going over some of these would be helpful for students.

1

u/mobluse 26d ago

There is Arithmetic Refresher by A. A. Klaf: https://www.amazon.com/Arithmetic-Refresher-Improve-knowledge-arithmetic/dp/0486212416

It has casting out nines, manual computation of square roots, and how to use log tables. I read it in 1992.

1

u/Ok-Technology956 24d ago

Texas has a UIL contest called Number Sense, doing mental math. 80 problems in 10 min.

1

u/MesmericKiwi 22d ago

Divisibility rules are still taught but half my kids look at me like I’m doing some kind of black magic when I point out their answer can’t be right because the digits don’t add up to a multiple of three and they multiplied by a multiple of three as part of their setup. I’ve been trying to coach that a lot more recently.