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.
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3 comments:
I love it! I can't wait to show my son. Thanks for sharing!
I don't know...it kinda smells a little bit like math to me. Cool math, but still math.
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
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