Another simple math shortcut

May 9, 2022 11:35:07 #

MrBob
Loc: lookout Mtn. NE Alabama

I prev. mentioned the Trachtenberg system of mathematics using shortcuts... Here is a simple one I really like.

Multiply any 2 digit number ending in a 5 by itself... i.e. 25x25 or 75x75.

Answer will ALWAYS end in 25 and first part of answer will be the original number x the next highest number.

example. 85x85 8x9=72 and ends in 25 SO, answer is 7225...

example. 45x45 4x5=20 and ends in 25 SO, answer is 2025...

The entire Trachtenberg system is full of little shortcuts like this. Enjoy...

Multiply any 2 digit number ending in a 5 by itself... i.e. 25x25 or 75x75.

Answer will ALWAYS end in 25 and first part of answer will be the original number x the next highest number.

example. 85x85 8x9=72 and ends in 25 SO, answer is 7225...

example. 45x45 4x5=20 and ends in 25 SO, answer is 2025...

The entire Trachtenberg system is full of little shortcuts like this. Enjoy...

May 9, 2022 11:50:11 #

chasgroh
Loc: Buena Park, CA

MrBob wrote: I prev. mentioned the Trachtenberg system of mathe... (

...and through this system my dad started doing square roots out of his head at the dinner table. Irritating!!! ;0) I've since tried to look it up, but spelling Tractenberg's name wrong didn't help. Thanks! (He told me that Jakow Trachtenberg was in a German concentration camp while creating this system...which turns out to be true. He was a Jewish Russian engineer.) Now to get the book!

May 9, 2022 13:31:59 #

May 9, 2022 14:13:56 #

Maybe this will help me with my dyscalculia and complete inability to do or comprehend math/

May 9, 2022 15:15:22 #

KindaSpikey
Loc: English living in San Diego

When in high school, we got a different teacher each year for all subjects. For one of those years we got a math teacher called Mr Wallis. He also happened to be one of the vice principles. He was a big scary man with a huge booming voice and a short temper. And back in those days, physical punishment was normal, so it was not unusual for us to get "the slipper", (beat on the butt with a tennis shoe), it stung, and the number of strikes depended on the "crime"! (chewing gum, talking when we were supposed to be quiet, etc), but it was not too bad. The next level of punishment was "the cane", (like a bamboo stick), and that thing really hurt! Number of strikes was again dependant on the "crime", (being rude to the teacher, fighting in class, etc), I was on the wrong end of both the slipper and the cane many times during my school years! (I swear I was innocent)! Anyway, I digress, despite all of that, Mr Wallis was an amazing math teacher and true mathematition. Some of us had calculators at that point, and were allowed to use them on special occasions. Mr Wallis used to issue challenges, one kid would shout out a math problem, multiply, division, equation, etc, and another pupil would work it out on their calculator, and Mr Wallis would work it out with his mind. Mr Wallis won, every single time, no matter how complicated the problem! He used to teach us "math tricks and shortcuts", which we were all in awe of. None of our other teachers had shown us anything like that! I've forgotten all of that by now, never really had a use for it after school, other than the usual, bills, taxes etc. But despite Mr Wallis being a big scary (seriously somewhat sadistic) man, he was the best math teacher we ever had! All the best,

Ray.

Ray.

May 9, 2022 18:15:43 #

MrBob
Loc: lookout Mtn. NE Alabama

chasgroh wrote:

...and through this system my dad started doing square roots out of his head at the dinner table. Irritating!!! ;0) I've since tried to look it up, but spelling Tractenberg's name wrong didn't help. Thanks! (He told me that Jakow Trachtenberg was in a German concentration camp while creating this system...which turns out to be true. He was a Jewish Russian engineer.) Now to get the book!

Yes, I understand he had no pen or paper and worked all these little shortcuts out in his head while in a concentration camp.... Actually, this one you can do faster without the calculator.

May 10, 2022 03:09:17 #

Laramie
Loc: Tempe

My senior year of HS, I had no idea of what I might study in college, but I had a calculus class with a nice old woman - I was 18, everyone was old - She taught me calculus and I understood it. So I studied math in college and did quite well, but was getting bored. Around Christmas I realized I would be 1 credit short of graduating, so I dropped out. Now I call it my sabbatical. I finished some time later, but never really used my training. When I tell this story people remark on how I could have made the mistake of being a credit short. I remind them that I was a math major, not an arithmetic major.

May 10, 2022 05:55:05 #

May 10, 2022 06:08:17 #

Delderby
Loc: Derby UK

MrBob wrote: I prev. mentioned the Trachtenberg system of mathe... (

My own Math shortcut converts degrees C to degrees F as follows - double the degrees C then take off 10%, and add 32. Use nearest integers!

Example: 24C x 2 = 48. less 10% (5) = 43, add 32 = 75F.

Also - 16=61 and 28=82.

Useful for the oldies like me who were brought up on Fahrenheit!

May 10, 2022 06:17:02 #

whatdat
Loc: Del Valle, Tx.

MrBob wrote: I prev. mentioned the Trachtenberg system of mathe... (

Took an elective course in high school called mental math. This is the only short one I remember.

β-Michael

May 10, 2022 07:08:15 #

May 10, 2022 07:22:07 #

Laramie wrote: My senior year of HS, I had no idea of what I migh... (

There are 3 kinds of mathematicians - those who can count and those who canβt count.

May 10, 2022 08:02:14 #

raymondh
Loc: Walker, MI

cdayton wrote:

There are 3 kinds of mathematicians - those who can count and those who canβt count.

I admit to being unacCOUNTable.

May 10, 2022 08:27:12 #

jerryc41
Loc: Catskill Mts of NY

My "shortcut" fits into my pocket and is powered by a tiny battery.

Numbers are fascinating, though.

Numbers are fascinating, though.

May 10, 2022 08:45:12 #

MrBob
Loc: lookout Mtn. NE Alabama

Delderby wrote:

My own Math shortcut converts degrees C to degrees F as follows - double the degrees C then take off 10%, and add 32. Use nearest integers!

Example: 24C x 2 = 48. less 10% (5) = 43, add 32 = 75F.

Also - 16=61 and 28=82.

Useful for the oldies like me who were brought up on Fahrenheit!

Example: 24C x 2 = 48. less 10% (5) = 43, add 32 = 75F.

Also - 16=61 and 28=82.

Useful for the oldies like me who were brought up on Fahrenheit!

Great one... I like it. Thanks for contributing... I actually long forgot the standard formulas we were taught for conversion...

If you want to reply, then register here. Registration is free and your account is created instantly, so you can post right away.