Wednesday, April 22, 2009

Works For Me: Eleven Times Table Trick

You're at the right blog, in case you thought you were lost. This is still me. The I Don't Do Math me.

But I have to share this little gem of math trickery with you! It is gold.

Gold.

Your kids will love you for this one.

Here's how to multiply 11 by a two digit number without your old Trig calculator.

Sample Problem- 11 x 23

Take the original number (23) and imagine a space between the two digits.


23


2_3

Now add the two numbers together and put them in the middle:

2_(2+3)_3


That is it - you have the answer:


253



If the numbers in the middle add up to a 2 digit number, just insert the second number and add 1 to the first: (This sounds more complicated, but will make sense once you try it.)


Sample problem- 11 x 99

9_(9+9)_9

(9+1)_8_9

Answer: 1089


Sample Problem 2- 11 x 89

8_(8+9)_9

(8+1)_7_9

Answer: 979

Math without math. What's next?

I'll still stick with English but, my word, this is cool. Even for a grammar geek.


Check out more tips over at We Are THAT Family.

3 comments:

Ann'Re @ Home said...

I love it! I can't wait to show my son. Thanks for sharing!

Nancy said...

I don't know...it kinda smells a little bit like math to me. Cool math, but still math.

pcb said...

I'm not a math person either and was so grateful when a teacher taught me the elevens trick. Same teacher also taught me the nines trick:

The digits in the answer always add up to nine with the first digit ascending and the second descending (up to 9x10, anyway...although there is a pattern for the ones after that, too).

9x1=9
9x2=18
9x3=27