The easiest and shortcut methods to do math using only human brain.....

[Mental Math]

 

 

The easiest and shortcut methods to do math using only human brain.....

 

Mental Mathwith Tricks and Shortcuts

 

 

[michel123456]

Entertaining blog. Well done.

[CaptainPanic]

It's a good blog... everybody should develop their own little tricks to calculate, and maybe this helps some people. For me, I have my own ways.

 

From the blog:

Dividing a large number by five is actually very simple. All you do is multiply by 2 and move the decimal point to 1 digit:

 

a) 195 ÷ 5

Step1: 195 × 2 = 390

Step2: Move the decimal: 39.0 or just 39

I find it easier to say that 195 is 5 less than 200.

200/5=40

So, 195/5 should be 39.

 

b) 2978 ÷ 5

Step 1: 2978 × 2 = 5956

Step2: 595.6

By now, with 4 significant numbers it depends on the work you do. For me the good-enough answer would often be "a bit less than 600", and the calculation would go something like:

 

2978/5 is a little less than 3000/5, which is a little less than 600.

 

You don't always need 4 significant numbers. But if you do, I am not sure that dividing by 5 is so much more difficult than multiplying by 2 and dividing by 10. Still, for some people this can be helpful, and you can never practice simple mental calculations too much.

Edited January 3, 2012 by CaptainPanic

[Mental Math]

Entertaining blog. Well done.

 

Thanks.

 

It's a good blog... everybody should develop their own little tricks to calculate, and maybe this helps some people. For me, I have my own ways.

 

From the blog:

 

I find it easier to say that 195 is 5 less than 200.

200/5=40

So, 195/5 should be 39.

 

 

By now, with 4 significant numbers it depends on the work you do. For me the good-enough answer would often be "a bit less than 600", and the calculation would go something like:

 

2978/5 is a little less than 3000/5, which is a little less than 600.

 

You don't always need 4 significant numbers. But if you do, I am not sure that dividing by 5 is so much more difficult than multiplying by 2 and dividing by 10. Still, for some people this can be helpful, and you can never practice simple mental calculations too much.

 

You are precisely right!

[michel123456]

I just remembered this old thread

http://www.scienceforums.net/topic/55999-mathemagic-arthur-benjamin/

[Brett Nortje]

I did model c maths. this was developed in my country south Africa in the eighties or so, and, it taught you to do all the maths in your head without paper, which means that working things out becomes more precise because there are fewer steps to go wrong with. of course, working everything out in your head can also lead to problems!

[daniton]

I know this things once I have read this book called Secrets of Mental Math by Arthur Benjamin and Michael Shermer which was great even in high school when we were celebrating Pi day under math club we use some of the tricks to entertain students.The book also has how to approximate square roots and great stories.

[ewmon]

I have my own modification to a method of mutliplication using fingers, and I have a simpler/easier method (than they teach in schools) of multiplying numbers on paper which forms an inverted triangle. It's simpler/easier because there are fewer "carries" and it works really well for squaring numbers.

[Mental Math]

Burning Math

Edited August 14, 2013 by Phi for All
Removed all the empty quotes