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10/2015
We're using this program right now, level 1. My daughter loves it so far.

Finding the Least Common Denominator


When adding or subtracting fractions with different denominators, you’ll need to find a common denominator. It is better to find the least common denominator so that there will be less work when it comes time to reducing the final answer.
“The least common denominator of two or more non-zero denominators is actually the smallest whole number that is divisible by each of the denominators.” (Help with Fractions.com)
When teaching my kids, I couldn’t pinpoint how to find the least common denominator, but rather just a common denominator (and sometimes they’d be huge!) So I went searching for methods, and this is what I have found.

For Younger Students:
Least Common Denominator Lesson from Math is Fun.com
Finding the Least Common Denominator (method of listing multiples)

Methods

Basically the same method illustrated in Ray’s Math:
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Finding the least common denominator – part of another lesson, scroll down after Google Ad. (similar method as above)
3 Methods for Finding Least Common Denominator
Take The Frustration Out Of Finding The Least Common Denominator ( Help with Fractions.com) – shows 2 methods for finding the least common denominator (very detailed)
From my daughter’s algebra book:
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Example using the above method:
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Tools
Least Common Multiple Tool – Nifty, plug in three numbers and get your least common multiple/denominator. Great for checking your manual work.
Games & Interactives
Least Common Multiple Interactive – simple, yet neat online activity where student must find the LCM/LCD of numbers. This might be a neat alternative to doing problems from your textbook. (Only a handful of problems, but most are application problems)
Least Common Multiple (LCM) Game – super old site, but nifty idea for making a card game.

Worksheets
From Teachnology.com:
  1. Least Common Multiples Worksheet 1
  2. Least Common Multiples Worksheet 2
  3. Least Common Multiples Worksheet 3
  4. Least Common Multiples Answer Key
Worksheet Generator:
SoftSchools.com LCM Worksheet Generator