Multiplying by 11

I have always been intrigued by the number 11. There has always been some unspoken magic regarding this number. I feel as though, more than any other time, I shoot a glance at the clock and it just so happens to be 11:11. I always make a quick wish in my head when I see this time. I have been unable to explain exactly why………

In class on Tuesday, Professor Antosz began speaking of the trick to multiplying by 11.  I for one had never heard of any such trick and was immediately intrigued. The good Professor went up to the blackboard and did a simple multiplication of 14 multiplied by 11. He wrote the number 1  4 on the board. Then with arrows below each number (1) and (4) multiplied them by 1 and then wrote them slightly spaced out. 1       4. Professor Antosz then placed a small + sign between the original 1 and 4, to look like this 1+4. The Professor took the sum of these two number and placed that number (5) in the space between the 1 and 4, to look like this; 1 5 4. BOOM!!!! This is the correct answer to 11 times 14. 

I was amazed, finally the number 11 and all its magic was showing its worth. Unfortunately, being as I am, incredibly pessimistic I wasn’t convinced. I needed more proof. I needed to see this work with larger numbers!! I decided to try, 8738 multiplied by 11.

 

I began by multiplying the first and last numbers by 1 and placing them at opposite ends. Next step was to add the numbers side by side together. I had to carry the 1 a couple times…. The result was……

 96118 the correct answer for 11 multiplied by 8738. Colour me impressed!




Looking back on the the outcome, the trick to multiplying any number by 11 works perfectly well. However, it does not work well with any other number. I played around for quite sometime seeing if any other number possessed the magic that 11 does. I unfortunately came up short.




In conclusion, the trick to 11 is great, fabulous, wonderful,..etc. But we must realize it only works for things multiplied by 11. I don't know about you, but how often in real life scenarios are we multiplying by 11? Groups are usually in 5, 10, or 12.  Even 13 when you ask for a bakers dozen. I do love the scenario for when I teach my grade 4 students their 11 times table. But any other time 11 is still 11...... That does not mean that I won't still be making little wishes when I catch 11:11 on the clock.