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To add or subtract fractions the denominators must be the same - then the numerators are added or subtracted with the denominator being kept the same.
When adding or subtracting fractions with different denominators, the fractions must first be converted into equivalent fractions with the same denominator and then the (new) numerators can be added or subtracted as required.
For the denominator for these equivalent fractions, the original denominators can all be multiplied together, but this can lead to having to work with very large numbers; a better choice for the denominator is the smallest number that all the denominators divide into, their Least Common Multiple (LCM) - this is is then used as the denominator for the equivalent fractions and is called the Least Common Denominator (LCD) of the fractions.
First you find the LCD okay??? Then you have to add or subtract. What they mean by that is that once you've found your lcd add or subtract..xx hope i helped :)
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Why would you want to rename fractions with the LCD?
Possible reasons: To add or subtract fractions, To compare fractions with different denominators.
Do you need to find the LCD in multipliying?
When multiplying fractions, it is not necessary to find the LCD first.
Why if there are two fraction having different denominator are you are going to find first their least common denominator?
To get the right answer when you add or subtract them.
Do you ever have to simplify if you find the LCD when subtracting fractions?
No because in order to subtract or add fractions the denominator of the fractions must be the same and if they are not then the lowest common denominator of the fractions must be found. Having subtracted or added the fractions then it may be possible to simplify the result.
How can using the GCF and LMC help you you add subtract and multiply fractions?
In order to add or subtract fractions, the denominator (bottom number) has to be the same. In order to make it the same, you find the LCM and multiply the fraction by whatever is necessary to make the denominator the LCM. FOR EXAMPLE: 1/3 + 2/5 The LCM of 3 and 5 is 15. To make the 3 in 1/3 15, you multiply the whole fraction by 5 over 5 (it simplifies to 1 so you aren't really changing the fraction by multiplying it by 1). 1/3 * 5/5 is 5/15 You multiply 2/5 times 3 over 3 using the same principle 2/5 * 3/3 is 6/15 NOW you can add 5/15 and 6/15 to get 11/15.
