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### Course: Arithmetic (all content)>Unit 5

Lesson 9: Common denominators

# Common denominators: 1/4 and 5/6

Learn how to find common denominators for fractions with different numerators and denominators by identifying multiples of the original denominators. It demonstrates the process using 1/4 and 5/6, showing that 12 and 24 can be common denominators.

## Want to join the conversation?

• Are LCM and LCD the same? I know the process for getting them IS the same, but I don't know whether they ARE the same. I know it sounds weird, but are they the same?
• They could be the same, depending on what LCD is.

LCM stands for Lowest Common Multiple. That's the smallest multiple that can divide every number in a set of numbers.

LCD could stand for Lowest Common Denominator, which would make it a type of LCM, and is just what we use in fraction LCM.

LCD could also be Lowest Common Divisor, which is exactly the same as LCM.
• Why is the entire piece or amount doubled?
(1 vote)
• The entire amount is doubled because you can't just only double the shaded area - otherwise your fraction isn't equally divided. It's kind of like simplifying or converting. 4/12 can be 40/120 or 1/3. If you only doubled the shaded part - you'd get 4/3 or something and your answer would be incorrect.
• Isn’t there also a trick where you can multiply the two denominators to get the common denominator? It has worked before for me but sometimes it doesn’t, why is that?
• Because sometimes the I common denominator/ LCM is the denominators times each other like 2/9+6/2 turns into 4/18+54/18 but if the problem is 5/6+3/9 you have to do a bit more work on that to turn it into 15/18+6/18
• wait . . . Isn’t there also a trick where you can multiply the two denominators to get the common denominator? It has worked before for me but sometimes it doesn’t, why is that?
• Multiplying the two denominators does not always give the lowest common denominator, but does always give a common denominator. Any common denominator (that is a multiple of the two denominators) can be used to add or subtract fractions, though using a common denominator other than the lowest one means that a greater amount of simplification is needed in the end.

Have a blessed, wonderful day!
• How do you solve a number like 7/12 -/+ 5/21? And find the answer?
• but how do you multiply them together
• you multiply the numerator by numerator and denominator by denominator
• Does anyone notice Sal gone?😳