Mental Math Multiplying Tricks
Tricks to mentally multiply by 9, 19, 99, 999, etc. The story of little Sophie Burnbomb.

Sophie B.'s Tricks for Nine
by: S.K. Martz Copyright 2001 themathlab.com
All rights reserved. No portion of this story may be used or reproduced in any manner whatsoever without written permission of themathlab.com, except in the case of brief quotations embodied in critical articles or reviews.


FACT: Most folks hate to multiply by nine and would never ever think of multiplying by 99 mentally. It's just too much of a pain. It's been a multiplicative pain for millions of people for hundreds of years. That's why little Sophie Burnbomb invented the Tricks for Nine.

She was a wild one, so she was.

You see Sophie was not your average, one room school house gal. No she had SPUNK beyond measure and brains to choke a cow!

She was short and perky, with fiery red curls and eyes so deeply green that they gave you the creepy feeling she could read your mind. Most of the kids in her class thought she COULD read their minds.

Yes she was a feisty one. She enjoyed nothing more than teasing the kids who she knew had lesser mental ability. No, take that back,...she DID love something more than teasing other kids. She loved to tease "old toad nose", Mr. Simpson her teacher, more than anything on earth.

Mr. Simpson in his younger days.

She believed him to be of inferior intellectual quality and she took every opportunity to demonstrate this to the class. She would catch him using improper English and tell him in front of everyone. She would correct his mathematical computation mistakes with obvious disrespect. Why one day she even told him that the front button of his trousers was missing and that he would simply have to refrain from teaching and go home to fix it. She said she absolutely could NOT concentrate with the distraction of possibly seeing his "private parts" peeking out.

Well, to say Mr. Simpson HATED Sophie Burnbomb was a grotesque understatement. He LOATHED the "fire-headed beast", as he called her behind her back. In fact he lived for the day when he would make her PAY for all of her disrespectful acts.

Finally the day came. Mr. Simpson had just finished explaining how to multiply seven hundred eighty-nine times nine. It took him an entire chalkboard of painstakingly explained work.

All the while he was explaining, he kept yelling out warnings to the class: "Make SURE you write down EVERY partial product in the APPROPRIATE spot. EVERY zero must be accounted for. If you are missing even one zero, you will get NO CREDIT for your answer, because it will be WRONG!"

He continued on and on with his threats of NO CREDIT and his warnings that the ONLY way to be successful with multiplication by nine was HIS WAY. When he was finished the black board looked like this:

ssss789
ssssx 9
-----------
sssss81
ssss720
+s6300
-----------
sssssss1
sssss100
ssss1000
ss+s6000
-----------
ssss7,101

When he finally stopped talking, he turned around slowly, puckered his lips, and looked at the class. He had the gleam of maniacal tyrant in his eyes. Yes, he had SHOWN them how to do it, and by GOD they would do it HIS way, OR ELSE.

Well this was simply more than little Sophie Burnbomb could take. She blurted out, "Why would ANYONE with a brain EVER multiply by nine like that?"

The class hushed, for this was the most disrespect they had EVER seen Sophia show. Why she was literally calling him brainless, in front of everyone!

Mr. Simpson's face became dark red as the blood rushed up to his neck, into his cheeks, and seemed ready to push out his eyes.

Sophie, oblivious to the danger approaching, continued on with her tirade, "Only an idiot would do all that work when nine is really just ten minus one."

Mr. Simpson slowly picked up his yardstick and began walking toward little Sophie. She didn't notice his approach as she found herself so excited by what she was thinking. She just HAD to show the kids how it would work.

She walked over to the side blackboard and with the genuine joy of discovery, she said this,"Yes,...look people,...if you don't think of nine as nine, but think of it as ten minus one, your troubles disappear. Because ten is easy to multiply by and one is the EASIEST number to multiply by. So instead of multiplying by nine, which is a pain, multiply by ten and by one in your head, and then subtract the two products."

She then showed the same problem Mr. Simpson had done using HER method:

789 x (10 - 1) = 7890
........................-.789
......................--------
........................7101

She said, "If you are good at subtraction, you can do the whole thing in your head!"

The kids in the class found themselves getting as excited as Sophie. This was the first time they had ever seen something so hard turn into something so EASY; and they really UNDERSTOOD it the way Sophie explained it.

Comments went flying through the room, "Wow,...That's great,...I bet it would work for 99 and 999 too,...Or maybe even 19 or 29,...Man, it's so much quicker,...Show us one with 99 Sophie!"

Everyone, including Sophie was so excited by this discovery that they didn't even see old Mr. Simpson slink up behind Sophie with his yardstick. He took her and the entire class by surprise as he yelled at the top of his lungs and smacked the yardstick down against her fingers, crushing them against the blackboard. A horrible thunderous, crack filled the room.

The whole class heard the bones in her fingers break a millisecond before her screams of pain. It all happened so very fast. One moment 42 minds were excited about truly discovering the power of number manipulation and in the next moment, 42 minds were paralyzed with mortal fear.


(Here is where it all happened.)

Well Mr. Simpson got his revenge all right. Sophie Burnbomb never returned to the one room school. No one really knows what happened to her.

That day, Mr. Thaddeus P. Simpson also murdered 39 young minds. You see the fear that was instilled by Mr. Simpson's yardstick and the sounds of Sophie's screams permanently scarred those minds. The scarring of their mental synapses forever prevented them from thinking and discovering for themselves. The negative association had been too fast and too strong.

The real horror of this story however is that these children grew up and passed this scarring on to THEIR children and their grandchildren too. Whenever any of their children showed an interest in math or in doing things a different way, they would be severely reprimanded with comments like: "NO! You do it the way I SAY! There is only ONE WAY to do math, and you will DO IT THAT WAY!"

Yes, they drummed this into their children, even with beatings sometimes, until finally the children, or most of them anyway, gave up and quit trying to use their minds.

Fortunately that is not the total end of this story. You see only 39 of the 42 minds in that class were murdered. First there was little Sophie, whose mind could never be crushed by the viscous, inferior minded Mr. Simpson. She was simply too spunky for that to happen.

Secondly, there were TWO OTHERS. Yes, two children in that class had been frightened like the other 39, but when they got home and talked to their parents about what had happened, the mental scarring was halted. In fact, they could even remember the excitement of seeing and UNDERSTANDING what little Sophie had shown them.

These two eventually found each other and began talking and thinking and growing in their minds. They left the one room school the next year and moved to High School. They were fortunate enough to meet a few others with sharp minds who had not been scarred by fear. Then in Sophie's memory, the Nine Tricks were formally written down and shared.

They tried to get others to see the elegance an ease of the Nine Tricks, but many people at the High School level wouldn't even listen or try them. These people had been scarred by their own fears too.

Slowly though, over the years the children and grandchildren of the group of creative math thinkers grew in number. Today if you look in the right places, you will actually see people doing ALL multiplication by nine like Sophie Burnbomb.

We at themathlab.com salute you Sophie! May your Nine Tricks live long and prosper!


EX: 37 x 9 =

Think: 37 x (10 - 1) = 370
...............................- 37
.............................-------
................................333

EX: 489 x 99 =

Think: 489 x (100 - 1) = 48900
................................... .- 489
..................................--------
................................... 48411

EX: 24 x 999 =

Think: 24 x (1,000 - 1) = 24,000
..........................................-24
....................................---------

...............................23,976

EX: 13 x 19 =

Think: 13 x (20 - 1) = 260 - 13 = 247

EX: 31 x 49 =

Think: 31 x (50 - 1) = 1550 - 31 = 1519

Use the Nine Tricks to find the eight products below. Then look in the password decoder box to find the letter that corresponds to each answer. When you list all eight letters in order, you will have the password to the treasure room.

When you KNOW the password

 

  1. 13 x 9 =
  2. 15 x 9 =
  3. 68 x 9 =
  4. 7 x 19 =
  5. 15 x 19 =
  6. 17 x 19 =
  7. 23 x 99 =
  8. 4 x 999 =
password decoder box
612
295
285
135
323
3,996
l
r
e
i
y
s
133
217
117
107
2,277
602
d
f
w
c
e
b

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