Math-Prof HOME Arithmetic Table of Contents Ask A Question PREV NEXT

Turbo Addition
Multiplication

 
 Multiplying is like high power addition. 
 When you multiply, you just add a number to itself a bunch of times.
 

 
 Examples:
 
5 times 3 means 5 + 5 + 5 = 15
2 times 4 means 2 + 2 + 2 + 2 = 8
3 times 2 means 3 + 3 = 6
4 times 1 means 4  (just one 4)
6 times 0 means 0  (no 6's at all!)
 
 Math type people LOVE to save space, 
 so instead of writing out the word "times" they use this symbol:
 

 X
 
 Hey wait a minute! 
 That looks a lot like the letter "X" !
 
 Well what do ya want maybe the math types were busy that day. 
 Anyway at least they used something easy to remember. 
 
 (Just wait till you get to Calculus! then you'll see some really weird squiggles!)
 
 So in math talk we write:
 
2 x 4 = 8 (2 + 2 + 2 + 2 = 8)
3 x 3 = 9 (3 + 3 + 3 = 9)
5 x 2 = 10 (5 + 5 = 10)
 
 Something funny happens with multiplication. 
 Watch this:
 
3 x 5 means (3 + 3 + 3 + 3 + 3= 15)
5 x 3 means (5 + 5 + 5 = 15)
     
4 x 6 means (4 + 4 + 4 + 4 + 4 + 4 = 24)
6 x 4 means (6 + 6 + 6 + 6 = 24)
3 x 7 means (3 + 3 + 3 + 3 + 3 + 3 + 3 = 21)
7 x 3 means (7 + 7 + 7 = 21)
 

HOW SPOOKY!

 This happens EVERY TIME. 
 That means when you multiply two numbers together, 
 you can write either one first. 
 The answer will come out the same.
 Sometimes when we multiply 2 numbers together 
 we write them like this:
 

 6 x 5 = 30
 
 But most of the time we write them like this:
 

 
 But either way it means:
 

 6 + 6 + 6 + 6 + 6 = 30
 
 I don't like to work at memorizing stuff. 
 I think that most of the time it's a dumb thing to do. 
 If you wind up using some info a bunch, 
 after a while you just memorize it.
 If you don't use the info  too much, 
 you wasted your time memorizing it in the first place. 
 
 One thing that IS worth memorizing is something called the times tables.
 You should TRY to memorize them up to ten times ten. 
 A good way to start learning them is to learn to count by each digit 
 up to about 10 times that digit.
 
 For example, count by 4's up to 40
 

 4, 8, 12, 16, 20, 24, 28, 32, 36, 40
 

   copyright 2005 Bruce Kirkpatrick
Math-Prof HOME Arithmetic Table of Contents Ask A Question PREV NEXT