NICE.
I want shortcuts for percentage,compound interest & A.P. , G.P.,H.P.series.
For easy math squaring shortcuts and multiplication shortcuts contact me at iforindia123@gmail.com
For example to show one of my methods:
To square a two digit number, say 74
7^2=49
(7*4)2=56
4^2=16
now add the digit other than the ones digit with previous number.
- 49 cant be added with a previous number.
- add the 5 of 56 with 49, 49+5=54 then simply attach the ones digit.becomes 546
- similarly add 1 of 16 with 546 and attach 6.
you get 5476.
this is the square of 74.
i.e. 74^2=5476
For easy math squaring,multiplication,Division,Addition,Subtraction, percentage shortcuts contact me at iforindia123@gmail.com
For example to show one of my methods:
To square a two digit number, say 74
7^2=49
(7*4)2=56
4^2=16
now add the digit other than the ones digit with previous number.
- 49 cant be added with a previous number.
- add the 5 of 56 with 49, 49+5=54 then simply attach the ones digit.becomes 546
- similarly add 1 of 16 with 546 and attach 6.
you get 5476.
this is the square of 74.
i.e. 74^2=5476 
http://mathshortcuts1.blogspot.com/ (Under construction)
Nice shortcuts, hope you could explain more of these if possible… 
I personally gravitate to the 68 mph is “about” the same as 100 fps is “about” the same as 30 meters per second. My logic…first off with the speed limit set at 65 mph you can generally travel at 68 mph and probably not get a ticket. So it is a velocity that we “know” and “feel”. More important however is that it makes it easier to envelop calculate the centripetal force formula of velocity squared divided by radius. Just a thought…nowhere near as profound as Khalid’s but a thought nonetheless
@mark: Really cool insight! I think it’s important to have a gut feel for numbers, and I think most people can “feel” how fast 65/68mph is (i.e. you have an idea of how fast things should be zooming past you on a highway).
best blog for knowledge
for shortkat for number of sqare for number thar have 5 at last like we take a number of 25 then
frist number we multiply subsiquint number and add the square of 5 for example of 25–
frist
(23)(55)
=625
Has anyone wondered why is that:
(a+b)^2 = a^2 +2ab +b^2
???
If you know why is it so, then you will become mental math multiplying champ
contact me at iforinida123@gmail.com
not nice.Apple rejected Google’s official Google Voice app from the App Store too. What is Apple thinking
A neighbour’s son brought this home: an explanation for the 9 x table (multiplication).
Both palms facing you, bend left- ring-finger towards yourself. It is the fourth digit from the left… so 4 x 9 = 36. What is displayed is your l-thumb, l-index, and l-middle finger = the three; and the one l-little finger and five digets on the right showing six total digets, displaying the 6 of ‘thirty six’. Only works on the 9 xtable. I have found it very useful.
Having discovered KhanAcadem.org, I can’t stop promoting it. Go to their website and watch the TEDtalk by Salman Khan. It blew my mind!
Khan Academy is a free online school. Had you heard about it before now?
V.V.Good
V.V.Useful
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Just a quick note, regarding all the nanos there are in the column.
One nano-century is (almost) pi seconds.
[…] Mental Math Shortcuts […]
@Raj
How to calculate x^y manually, is there any short cuts?
Using logarithms and antilogarithms you can.
Quick calculations with a few logarithms
If you can remember a few logarithms, you can do many calculations quite easily without the aid of calculators or computers.
Try to remember the logarithms of just seven numbers:
Log 2 = 0.30, log 3 = 0.48, log 7 = 0.85, log 11= 1.04, log 13= 1.11, log 17 = 1.23 and log 19=1.28.
The logarithm of a composite number is equal to the sum of the logarithms of its prime factors; you can formulate the following table of logarithms:
Number Logarithm Number Logarithm
2 0.30 11 1.04
3 0.48 12 1.08
4 0.60 13 1.11
5 0.70 14 1.15
6 0.78 15 1.18
7 0.85 16 1.20
8 0.90 17 1.23
9 0.95 18 1.26
19 1.28
Note: Logarithm of 11 is 1.04. It means log 1.1 = 0.04. Log 5 = log (10/2) = log10 – log 2.
With the above figures in hand you can do a lot of calculations quite easily.
- What is 2 raised to power 37?
Logarithm of 2 is 0.30.
37 times 0.30 is 11.10
Since logarithm of 1.2 is 0.08 and logarithm of 1.3 is 0.11, antilog of 0.10 is about 1.26.
So antilog of 11.10 is 1.26 * 10^11.
That is 2^37 = 1.26 * 10^11. - What is the 31st root of a 35 digit number?
This can be answered even without knowing the number.
Log of 35th digit number is 34. …
Log of 31st root = 34. …./ 31
This lies between 34/31 and 34.99/31 or between 1.09 and 1.13.
From the above table, we can see that in this interval, logarithm of 13 is 1.11.
So, 31st root of a 35 digit number is 13. - What is the 64th root of a 20 digit number? Answer is 2.
- What is the cube root of say 74567?
Log of 74567 = 4.873 (interpolating between log 7 =0.85 and log 8 = 0.90).
4.873 / 3 = 1.624.
Antilog of 0.624 is 4.24 (because log 4 = 0.60 and log 5 = 0.70).
So, cube root of 74567 is about 42.4
how to find cube of three digit number?
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