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Multiply Numbers in Your Head Really Fast

Updated on May 31, 2010

Impress Your Friends

When people learn the multiplication tables in 3rd grade (I think that is when they do it), they memorize numbers up to a 10x10 matrix and sometimes a little higher. There was a time that it was a need for people to be able to do basic arithmetic in their heads.  Unfortunately people now rely on calculators which means that people do not gain the ability to have a feel for numbers. When a number is higher than this 10x10 matrix, many people cant multiply it in their heads.  Most people have become mathematically lazy. A person who can multiply two double digit numbers in their head will also impresses people. It is not hard and here is a trick to make it easier. You can impress others and  be thought of as super smart. People will think this by the way.

So we are going to assume that a person has a knowledge of all multiples is a 10 by 10 matrix.

Lets start with all the squares. 11x11=
Here is how to do it in your head:

1x11=11 and 10 x 11 =110

Not too bad but some may not see this at first so lets discuss it. We have a 2 digit number 11 and it is composed of a 10's digit and units digit. If we break 11 into 10 and 1 it is easy to multiply and fairly easy to add in our heads. The part that is hard when multiplying numbers in our heads is remembering all the numbers and placing the numbers in their corresponding slots (ie thousands, hundreds, tens, and units).  The more digits we have the harder it becomes to keep track of these numbers in our head.  We need something to help us. 

I will expaln this as we multiply 12 x 12. How hard is it to multiply 12 by 10? It is not hard at all. How hard is it to remember? Not hard at all. 12 x 12 is equal to 24 + 120=144. What you are doing is multiplying 2 by 12 and getting 24 and knowing that you will add this to 120.

So lets do some more:

17x17=119+170=289 (This is a little harder)

Now when we multiply the units digit by a 2 digit number  and the resultant number has three digits it bcomes  a little harder.  This is because we typically don't learn these numbers in our math classes. However, don't let this stop you. You have 3 numbers to memorize right. Not a 100 like you did when you memorized your times tables.

Now lets say that we have 12 x 18, we do this in the same fashion but it is not a square. This looks like:

96 + 120=216 or how about 36 +180=216. Smaller number that result from the units digit result will be easier to utilize.

If it is hard for you to mulitply a one digit by a 2 digit number with a three digit resultant here are some numbers for you to memorize:

6x17=102, 6x18=108, 6 x 19=114
7x15=105, 7x16=112, 7x17=119, 7x18=126, 7x19=133
8X13=104, 8x14=112, 8x15=120,8x16=128,8x17=136,8x18=144, 8x19=152
9x12=108, 9x13=117, 9x14=126, 9x15=135, 9x16=144, 9x17=153, 9x18=162, 9x19=171

That is not a lot to memorize but I can hear the groans as well as the boos and hisses. So lets just learn a methodology so we don't need to remember. Okay?

The easy part will always be the tens digit. Remember this and forget about the 10's digit for now. Say that you want to multiply 17x19.

Lets look at 7x 9=63 and 7 times 10 =70. 70 +63 is 133. Like clockwork we have 133 in our heads and we can easily add this to 190. Our answer would then be 323.

The key is to not juggle too many number in our heads. Years ago people had to use numbers and more people where able to do basic multiplication in their heads. A person who practices this 30 minutes a day for week shoud have it mastered.

This will impress people. I guarantee it. This will help with tests like the ACT and SAT and a good feel for numbers will actually help a person comprehend higher order math like calculus.  It is also good for the brain and will help a person understand numbers as well as increasing his/her memory.


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    • profile image

      lola 5 years ago

      Sorry for the earlier comment that was my brother he thinks he is the best speller in the world. Your writing is awesome, it really helped me for my math test tomorrow.

    • profile image

      lola 5 years ago

      you can not spell, my sister can spell better than you hmmmm... oh wait did i mention she is in 2ND GRADE.

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      Amit jha DreamBoy 6 years ago

      this is suuuuuupppppppppeeeeeeeeeerrrrrrrrrrrbbbbbbbbbbb !!!!!!!!!!

    • Ben Evans profile image

      Ben Evans 7 years ago

      I am glad that you can utilize this. I am going to do a post or posts on prime numbers up to 1000. There are a couple of tricks to figuring out if a number is prime.

      thank you for reading

    • acaetnna profile image

      acaetnna 7 years ago from Guildford

      I was totally fascinated by this hub. This is brilliant and I am so pleased I found you.I am definitely bookmarking this to remind me.Thanks so much.

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      xxrocknrollxx 7 years ago

      Thanks but i need is 2 learn my 12's and im done!!!;D

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      sha x 7 years ago

      thanks, its terrible, i was revising A* quadratics for my math gcse, and realised i have forgotton how to do the basics!

    • Ben Evans profile image

      Ben Evans 7 years ago

      Hey thanks. I hope people can learn to do this and it is easy.

    • billyaustindillon profile image

      billyaustindillon 7 years ago

      Great tool - thanks this will come in very handy.