i'm struggling with mental arithmetic..could you guys give me some short tips to do fast mental arithmetic?and thanks!

Question

i'm struggling with mental arithmetic..could you guys give me some short tips  to do fast mental arithmetic?and thanks!

hartnn · Answer

see some @AravindG tutorials on vedic maths.

sepeario · Answer

http://tedmuller.us/Math/MentalArithmetic.htm

parthkohli · Answer

What I do for addition is this:$$63 + 45 = 60 + 40 + 5 + 3 = 100 + 8 = \boxed{108}$$For multiplication,$$21 \times 23 = 21\times20+21\times3 =420+63=\boxed{483}$$For subtraction,$$145 - 87 = 145 - 80 - 7 = 65 - 7 = \boxed{58}$$

parthkohli · Answer

For division:$$168\div 21 = (84 \div 21)\times 2 = 4\times 2 = 8$$

theviper · Answer

nice explanation @ParthKohli :)

parthkohli · Answer

Though it's just tricks. You need to discover these, and believe it or not: The first three tricks were discovered by me... and I didn't look 'em up!

parthkohli · Answer

Thanks @TheViper! =)

theviper · Answer

U deserved that :D

parthkohli · Answer

Another thing that I do for division is this:$$558\div 8 = 279\div 4 = 278\div 4 + 1\div 4 = 69.5 + 0.25 = 69.75$$

theviper · Answer

http://www.wiziq.com/tutorial/26654-Tricks-for-Faster-Maths http://www.youtube.com/watch?v=hLdKsKep1og http://listverse.com/2007/09/17/10-easy-arithmetic-tricks/ http://mental-maths-trick.blogspot.in/2011/10/do-super-quick-maths-calculation-using.html

parthkohli · Answer

On the contrary, I think that there's is nothing wrong with being slow with mental arithmetic; so is thought by Stephen Wolfram.

parthkohli · Answer

And Conrad Wolfram.

parthkohli · Answer

http://www.youtube.com/watch?v=60OVlfAUPJg

anonymous · Answer

wow..thanks guys..thanks @parthKohli @TheViper  @Sepeario @hartnn ..i dont kno wat to say..thanks...

theviper · Answer

:)

hartnn · Answer

21*23 = 22^2-1 = 484 -1 =483
anything *25 = anything*100/4

parthkohli · Answer

No problem!

parthkohli · Answer

Yeah, and... $n \times 5 = 10n/2$.

anonymous · Answer

@hartnn sorry ii dint get u...

parthkohli · Answer

@mathavraj: It's a method described in Class 8 NCERT.

anonymous · Answer

hm well i was not under ncert syllabus..

hartnn · Answer

21*23 = (22-1)(22+1)=22^2-1^2 = 484-1
25*36 = 3600/4 = 900

parthkohli · Answer

$$21\times 23 = (22 + 1)(22 - 1) = 22^2 - 1 = 484 - 1  = \boxed{483}$$

hartnn · Answer

i have so many tricks to share....but not now.

parthkohli · Answer

It's easy to multiply by any multiple of $5$.

To multiply by 5, put a zero then halve.
10: put a zero or shift the decimal to the right.
15: $n \times 15 = n\times10 + n \times 5$
20: multiply by 2, put a zero.

parthkohli · Answer

And so on...

hartnn · Answer

look up multiplication by series of 1
multiplication by series of 9
they are pretty simple.

anonymous · Answer

i understand u @hartnn ...do it as u pls..

parthkohli · Answer

Oh yeah, another thing which Hartnn reminded me of!$$9n = 10n - n$$$$8n = 10n - 2n$$.
.
.

parthkohli · Answer

$$9\times62 = 62\times10 - 62 = 620 - 62 = \boxed{558}$$

hartnn · Answer

multiplication by 9, 99, 999 .....even 9999999   ...can be done in seconds, mentally

parthkohli · Answer

Use the rules of algebra and apply those on numbers: Variables are just numbers in disguise!

anonymous · Answer

@hartnn how?

anonymous · Answer

parth yeah u r rit..

parthkohli · Answer

@mathavraj $999n = 1000n - n$, $9999n = 10000n - n$... :P

hartnn · Answer

there's an another shorter way....|dw:1357471037933:dw|