HarvardHomemaker

By HarvardHomemaker

I'm a Harvard graduate and homemaker who blogs about living (and loving!) the domestic life with my husband and four young daughters. My blog now permanently resides at www.harvardhomemaker.com. Please visit me there!

Posted on Friday, March 29, 2013 at 09:17:00 PM in Tips & Tricks
Tags: education,  kids,  school,  math,  friday fast tip

Multiplying by 9 Trick

Many of you probably know about today's tip, but if this is one you have never seen before, buckle your seatbelt!!  You're going to wish you'd had this trick in your back pocket when learning how to multiply!  Obviously anyone learning how to multiply must understand the concept; but once that part of it has been accomplished, sheer memorization takes over.  I always thought memorizing the "nines" was the hardest--until someone taught me this trick.  

It works like this:

1)  Hold out both of your hands, palms down.

2)  When multiplying single-digit numbers by nine, you count from left to right and put down the finger that corresponds with the number by which you are multiplying.  For example, if I am multiplying 9x5, I will count from left to right, and my thumb will be the fifth finger.  I will tuck my thumb under to indicate the break.

3)  If you try it, you will see that you have 4 fingers remaining before the break; and you have 5 fingers remaining after the break.  Thus, the answer is 45.

See the pictures below to illustrate what I'm trying to describe.

As a third grader, I can distinctly remember playing "Around the World" where one student would stand next to another student's desk.  The teacher would hold up a flashcard with a multiplication problem on it, and the student who came up with the correct answer the fastest moved on to the next desk.  I would cross my fingers that I'd get a problem with "9" in it every time!!  If I was so lucky, I'd fly my hands up in front of me and shout the answer in a flash!  Everyone was always trying to figure out what the heck I was doing with my hands!  The secret's out now!  :)

I hope this little tip is helpful to your kids, students, or maybe even you!  Cool, right?!  When I taught this to my daughter last year, a smirk spread across her face... After that moment, I'm pretty sure she was hoping to get a problem with "9" in it, too, when their class would play Around the World!  I guess the apple doesn't fall far from the tree!  :)

P.S.  Around the World is a great game to play in the classroom.  You can play it as described above with math problems of any kind, but you could also come up with any type of question that needed an answer:  telling time, geography, reading comprehension, etc.  It's fun for students to see how far they can get before someone beats them out and takes their spot!

9x7=63. Can you see how my daughter put her seventh finger down? That left 6 fingers before the break and 3 fingers after the break. Thus, 6 and 3 would tell her the answer is 63.

Here's another example. 9x9=81. Can you see how my daughter put her ninth finger down? That left 8 fingers before the break and 1 finger after the break. Thus, 8 and 1 would tell her the answer is 81.

What educational tricks can you share?

Thanks for reading my second "Friday Fast Tip!"  I almost forgot it was Friday today... just about messed up already on only my second week of this new series!!  Oops!  I still have two hours to spare, though... :)  (A wild and crazy Friday night apparently for me!!)

Until next time... have a great weekend, my friends!

HH

 

 

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