Math Is Fun Forum

CyclonEnigma

Member

Registered: 2007-07-11

Posts: 1

How to do mental calculations

This is a simple trick for multiplying

Let say:

39x45

39x4=156
39x5=195

156
  195
_____
1755

Now how about three digit by three digit:

362x284

362x2=724
362x8=2896
362x4=1448

724
2896
   1448
_________
102808

If the multiplication of the first number and the first digit of the second number is a three digit product then most likely the answer is a 5-digit answer

Math_Girl

Member

Registered: 2007-07-27

Posts: 23

Re: How to do mental calculations

That's not bad but this is a really good method also

http://www.youtube.com/watch?v=YFvwRzjTWAw

http://www.youtube.com/watch?v=sd_Bub5jEJY
^This one is very good too!

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"Genius is 1% inspiration and 99% determination"