Here's our first MATH lesson. It is so easy that one night, I wound up showing it to everyone in the pizza restaurant. Well, everyone who would listen, anyway. We were scribbling down the answers right on the pizza boxes with such excitement that I couldn't help it - I started laughing right out loud about how excited everyone was about math... especially on a Saturday night.
When you do this calculation in front of friends or family, it's more impressive if you hand a calculator out first and let them know that you are 'testing to see if the calculator is working right'. Ask for a two digit number and have them check the calculator's answer against yours.
If you really want to go crazy, you can have math races against the calculator and its operator, just as the Arthur Benjamin video shows. (Only you don't need to do the squaring of five-digit numbers in your head!) Have fun!
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Download Student Worksheet & Exercises
So here's the deal:
11 x 23 = ?
Take the 23 and spread it apart, so it looks like "2 3" with a space in the middle. Now add 2 + 3 to get: 2 + 3 = 5 and insert the 5 into the space. So...
11 x 23 = 253
That's it. How cool is that??
What about this one? 11 x 45 = ?
Spread apart the 4 and 5, then insert the sum of the 4 and 5 in between to get:
11 x 45 = 495
Whoa...!!! This stuff is soo cool! But wait a second... you hit a speed bump when you try this one:
11 x 86 = ?
It seemed a bit ridiculous to get: 11 x 86 = 8146. The answer should be a 3-digit number, not 4! So, check again and then find that you need to 'carry' the one to the first digit, so it becomes:
11 x 86 ==> 8(14)6 ==> = 946
And of course, if you can do 86, you have to give 99 a try:
11 x 99 ==> 9(18)9 ==> 1,089
Now you give yourself a few different numbers to try. Check your answer with a calculator!
Tell me how YOU think this works in the comment field below!
Exercises
- 11 x 11
- 11 x 27
- 11 x 43
- 11 x 49
- 11 x 50
- 11 x 67
- 11 x 79
- 11 x 89
- 11 x 92
- 11 x 96
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You should have access to this section of the program. I will have my team contact you right away!
My son started with the multiplying by 12, he got the download part and it said stop and do multiplying by 11 if he had not done that first. He went there and it said he does not have access. It seems that is the case for everything he has tried to do so far. What does he need to do to use this program?
Sincerely The Stark Family
learned this on school house rock as a kid… loved teaching it to my own kids years ago.
Yes, that’s on our resources page for Math – I’ve spoken with Dr. Benjamin and he’s such a blast!
If you like that-try his lecture “The Joy of Mathematics” from the Teaching Company, 24 jlorious math lectures.
Wow! You have opened my eyes! Thank you for showing us this secret! I wish my math teachers would’ve taught this to us in school!
This is awesome!
MAX SPEAKING: wow aroura i’m not sure how to spell that but this is the greatest thing ever.MAX SPEAKING:please follow me on facebook.com my user name is javenojave and i sent you a friend requist so u can accept it thank u bye 🙂
thats so cool!
OMG! I am so lousy at multiplication without a calculator any more and now at least I can do the elevens. How COOL is that! thank you.
By the way…this is Rebekah’s mom now Rebekah.
i am so happy that I stumbled upon your site…..its really interesting…….i’m thoroughly enjoying the videos
We tried to make this difficult but it isn’t all!
Cool! So glad she’s excited! If you need help, check out this section for 3-digit multiplication.
Aces! After showing this video to my daughter she decided she wanted to do a “Magic Math” presentation to her class! Then the wheels started turning and she wanted to see if the same method would work for 3 numbers! Love to see her THINKING and PROBLEM SOLVING!
This is really neat.