
Multiply By 11 Expanded 9 X Rule Square a 2 Digit Number Ending In 5 Square a 2 Digit Number Multiply By 4 Multiply By 5 Multiply Up to 20X20 In Your HeadIn just FIVE minutes you should learn to quickly multiply up to 20x20 in your head. With this trick, you will be able to multiply any two numbers from 11 to 19 in your head quickly, without the use of a calculator.I will assume that you know your multiplication table reasonably well up to 10x10. Try this:
Want to Learn More?The one book I recommendMay be out of print "Super MathEMagics" by V.A. Stephen Lenaghan
The 11 RuleYou likely all know the 10 rule (to multiply by 10, just add a 0 behind the number) but do you know the 11 rule? It is as easy! You should be able to do this one in you head for any two digit number. Practice it on paper first!To multiply any two digit number by 11:
The only thing tricky to remember is that if the result of the addition
is greater than 9, you only put the "ones" digit in the hole and carry the
"tens" digit from the addition. For example 11 x 57 ... 5__7 ... 5+7=12 ...
put the 2 in the hole and add the 1 from the 12 to the 5 in to get 6 for a
result of 627 ... 11 x 57 = 627
Finger Math: 9X RuleTo multiply by 9,try this: (1) Spread your two hands out and place them on a desk or table in front of you. (2) To multiply by 3, fold down the 3rd finger from the left. To multiply by 4, it would be the 4th finger and so on. (3) the answer is 27 ... READ it from the two fingers on the left of the folded down finger and the 7 fingers on the right of it. This works for anything up to 9x10!
Square a 2 Digit Number Ending in 5For this example we will use 25
Try a few more 75 squared ... = 7x8=56 ... put 25 behind it is
5625.
Square 2 Digit Number: UPDOWN MethodSquare a 2 Digit Number, for this example 37:
With practice this can easily be done in your head. Thanks To Ryan
Multiply By 4To quickly multiply by four, double the number and then double it again. Often this can be done in your head.
Multiply By 5To quickly multiply by 5, divide the number in two and then multiply it by 10. Often this can be done quickly in your head.
The 11 Rule ExpandedYou can directly write down the answer to any number multiplied by 11.
Some Math/Education/Parent/Kid LinksWebSchooling(Great Study Resources) Dave's Math Tables Students on the Net: Free Resources Pedagonet  Learning Resource Center Computer Lessons for Children and Young Adults Mr. Titen's: More Than Math Page Kid Safe Portal To The Internet Check back soon!I will add new tips every so often! Your Opinion Please!
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