My methods for Addition , multiplication explained here:
the addition is basis and grouping numbers works well for me
1 5 4 8 5 9 3 9 5 4 4 5 4
i try to group numbers , groups of values 5 10 15 20 …
first 3 is 10
next 4 is 25 so we have 25+10
i see 4 times 3 so 35+34=47
and 25+9 we have 47+19=66
there are many videos from Youtube and others for multiplying 2 digits numbers
2458 = (25)(45+28)(84)=1392
but it’s hard for 3 digits numbers(or say better it takes time) i am sure even Arthur T. Benjamin never use such methods while those methods rarely used.
when some one asks you to answer 5479 the best time for you is 5 seconds and the maximum time is 10 seconds.
by memorizing different methods of multiplying for different numbers and choosing the best one when some one asks you a question takes more than 10 seconds.
so prodigies in mental math never use these methods like:
the brain is the same!
good methods and hard training makes them a good calculator.
one of the questions in World mental calculation 2010:
i have done this in 20 minutes!(with the best conditions and full concentration!)
it was interesting for me that my answer was correct! by calculating and memorizing numbers from right to left but the time kills the questioner as well.
it’s like this:
your good friend asks you to calculate the 1548*6231 and you tell him: hey! please wait
some moments(each moment = 2 minutes) and drink a cup of coffee and watch a football game on tv then comeback to me happily and i will give you the answer
even it’s more disappointing to tell him not exactly but maybe the answer is 9645588
any one with a good method of multiplying please share it!