Ciphering in your head

[Jogeephus]

Here is a little trick I thought some of you might find useful in everyday life. It has to do with a quirck in mathematics and you might find it helpful from time to time. I'll give you the basics of it but it can be expanded with a little ingenuity. First of all, whenever two two digit numbers say between 10 and 100 begin with the same number and the sum of the second two numbers add up to ten, this trick can be used flawlessly.

For instance, if you need to know the sum of 75 x 75, forget all the multiplication you have been taught and just multiply the two fives together to get the number 25. Next, add 1 to one of the 7's and you get 8. Multiply 8 x 7 and you get 56. Now jut put these two numbers together and you get 5625.

Take 83x87. 8x9=72 3x7=21 answer is 7221.
Take 91x99 9x10=90 9x1=09 answer is 9009.

Or what is the 75 squared? 56 25

Get the drift? But remember, the first two numbers HAVE to be the same and the last two HAVE to add up to 10. But once you get the hang of this, you can expand this even further to numbers that almost meet the rule.

Hope this is a worthwhile tip if not, maybe you can win a beer with it.

 

[bigbull338]

ive always done math off the top of my head.an im not just talking lil figures.i can do pretty big figures.dont have time to use the calcalater.

 

[pdfangus]

I am a little slow .....so it is easier for me to pull out a pencil and do it the old fashioned way than it is to try to rememeber the trick.

 

[1982vett]

Hard enough remembering two numbers much less ciphering in my head. :dunce:

 

[alabama]

Good tip.
It seems that everywhere you go they are giving away calculators and advertisements. I got those cheep things stuck everywhere. Tractor boxes, trucks, almost always in my pocket and in every desk in the house. Back when I was in school I could do fairly well in my head but this old head has grown dependent on caculators. Good thing they are cheep.
I remember the first calculator I had. It was made by Texas Instrument and did less than the cheep ones today. That thing was $150 and that was back in 1972 or 74 dollars.

 

[ga. prime]

:lol2: :lol2: Jo, that is an insanely unworkable trick!!!!!!

 

[Jogeephus]

:lol2: :lol2: Jo, that is an insanely unworkable trick!!!!!!

:?: What do you mean by unworkable?

 

[skyline]

Jogee, that's a neat trick. Do you remember the movie The Rainman? You're not that character that Dustin Hoffman played are you?

 

[Jogeephus]

Jogee, that's a neat trick. Do you remember the movie The Rainman? You're not that character that Dustin Hoffman played are you?

No, I'm afraid I don't look that good in a suit and tie.

 

[skyline]

Jogee, that's a neat trick. Do you remember the movie The Rainman? You're not that character that Dustin Hoffman played are you?

No, I'm afraid I don't look that good in a suit and tie.

Ha! But he could sure do some ciphering....

 

[ga. prime]

:lol2: :lol2: Jo, that is an insanely unworkable trick!!!!!!

:?: What do you mean by unworkable?

Wrong word on my part. I'm too old to learn that trick is what I guess I'm trying to say because I could do the math in my head quicker than I could decide if two numbers met the criteria for your trick to work. Probably a good trick to learn if you're young. Just speaking for myself. Should have kept my mouth shut.

 

[Jogeephus]

No problem, I thought maybe you chose a set of numbers that didn't work. Haven't found any yet but there's always that chance. It takes a little practice to use but once you get the hang of it its quicker for me than a calculator and I have won a few bets with it. ;-)