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Transcript
Bell Ringer
• What is a prime number?
• What is a composite number?
• Give an example of each.
Greatest Common
Factor
Mr. Haupt
CC.2.1.8.E.1
Greatest Common Factor
• The Greatest Common Factor, or GCF, is the largest number
that goes in to every number given.
• For example, the GCF of 12 and 16 is 4.
• To find the GCF, you need to know the difference between
prime and composite numbers.
Prime Numbers
• Prime numbers are numbers where the only factors, or ways
to multiply, are one and the given number.
• For example, the number 17 can only be broken down into one
times 17.
• Other examples: 1, 2, 3, 5, 7, 11, 13, 19, 23, 31, etc…
Composite Numbers
• Composite numbers are basically numbers that are not prime.
• So, they are numbers that have more multiples than just one
and itself.
• For example, the factors of 28 are:
• 1 x 28
• 2 x 14
• 4x7
Prime or Composite?
• 89
• 21
• 33
• 97
Prime Factorization
• Prime Factorization is breaking a number down into its
smallest (prime number) factors.
• I find it easiest to use a factor tree.
• 30
54
What if we add letters?
• Nothing changes, except now we have to write out the letters.
• 45a2b3
36c3d
GCF, finally!
• So finally, we can get to the actual GCF.
• To find the GCF, we have to do the prime factorization of each
number given.
• Then we take all the prime numbers they have in common,
and multiply them.
• Our answer is the GCF.
For example…
• Find the GCF:
• 36 and 45
• 28a2b and 35ab2
A few more…
• 88 and 44
• 64a2b2 and 96a2b