​Finding Greatest Common Factor (GCF)

​-Make factor trees of both numbers: Split off as you work your way down finding primes(think 2,3,5,7,9,11)

​

​-Find common factors and multiply: Find the common prime factors that are present in both numbers. DOn't miss multiples of them. Then multiply those primes.

​-That's it... you've found the GCF

​Finding the Least Common Multiple (LCM)

​-Make a factor tree: Same as with GCF, make a factor tree of primes. I like to split to the right.

​- Find greatest occurrence of each distinct prime numbers. Multiply them

​- Notice we used both two's... we needed greatest occurrence.

​When do we use GCF and LCM

​LCM

​Used to find common denominators

​---Word Problem Signal Phrases---

​

​Repetition

​cycles/patterns

​two things - happening at the same time

​smallest or least number of sets

​GCF

Used to reduce/simplify fractions

​​---Word Problem Signal Phrases---

​groups or sets no remainder

​splitting/dividing equally

​Share

​No Leftovers

​Greatest or Largest

LCM​

Because we are looking for two or more things happening at the same time. ​

Greatest Common Factor​

​The question had greatest in it and it asked us to divide something

​LCM's and GCF's

​Hopefully after this quick refresher you are now ready to tackle any word problem that uses one of these two strategies.