November 10, 2010

The Cake Method is a way to find the prime factorization and even least common multiple

It's called the cake method because it looks like an upside down layered cake.

Even numbers are divisible by 2

Is zero divisible by 2? Yes

What are odd numbers?  Numbers that are not divisible by 2.

Divisibility Rules

• 2 - if the number is an even number, then that number is divisible by 2
• 3 - the sum of the digits of a number is a multiple of 3, then the number is divisible by 3.  Example:  7491 = 7+4+9+1 = 21, 21 is a multiple of 3, so 7291 is divisible by 3
• 4 - if the last two digits of a number are divisible by 4, then that number is divisible by 4. or  Half half rule.  If you can half those last two number twice, then the number is divisible by 4. Example; 48 divided in half is 24, 24 divided in half is 12.  48 is divisible by 4. (up to 100)
• 5 - if the number ends with a zero of 5, then the number is divisible by 5
• 6 - If the number is divisible by 2 and 3, then the number is divisible by 6
• 8 - look at the last 3 digits of the number, cute them in half.....cut in half again.....cut in half again...if you can cut that number in half 3 times, the number is divisible by 8. (up to 100)
• 9 - add all of the digits, if the sum is divisible by 9 then the number is divisible by 9
• 10 - if the number ends in a zero, then that number is divisible by 10
• 11 - if the last two digits of a number are a double number for example; 44, 55 or even 66....then the number is divisible by 11.

Forehead Multiplication Game (Name is still in progress, input is welcome) 

• Needed:  one deck of cards, but take out the aces and face cards
• students get in groups of 3
• one person is the captain
• the captain draws two cards, and multiplies the two together (without showing the two cards to the other students)
• captain hands the cards to the other two players face down
• captain the says the product as the two players hold their card on the forehead.  (the two players don't see what their card is.  They can only see what the other player has.)
• Students then have to figure out what their card is.  
• The student who says their number first and accurately gets to keep the cards,
• The player with the most cards at the end wins and gets to be the captain.